DATA USERS GUIDES 1: Digital Line Graphs from 1:24,000-Scale Maps 2: Digital Line Graphs from 1:100,000-Scale Maps 3: Digital Line Graphs from 1:2,000,000-Scale Maps 4: Land Use and Land Cover Digital Data from 1:250,000- and 1:100,000-Scale Maps 5: Digital Elevation Models 6: Geographic Names Information System 7: Alaska Interim Land Cover Mapping Program Data Users Guides 1-7 generally replace the Geological Survey Circular 895. Questions regarding availability and ordering of US GeoData (all types of digital cartographic and geographic data produced and distributed by the U.S. Geological Survey) should be addressed to: Earth Science Information Center U.S. Geological Survey 507 National Center Reston, Virginia 22092 (703)860-6045 (800)USA-MAPS Technical questions and comments should be addressed to: Branch of Technical Management U.S. Geological Survey 510 National Center Reston, Virginia 22092 UNITED STATES DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY DIGITAL LINE GRAPHS FROM 1:2,000,000-SCALE MAPS Data Users Guide 3 Reston, Virginia 1990 First printing, 1986 Second printing (revised), 1990 1 CONTENTS- Page Introduction 3 Data content 4 Data structure 5 Levels of structuring 5 Topology 5 Topological elements 5 Attribute codes 6 Major attribute codes 7 Minor attribute codes 8 Sample line graph structure 11 Graph theory in DLG data 13 Distribution formats 17 Source materials 18 Cell size and file extent 19 Coordinate systems 19 Standard distribution format 19 Optional distribution format 20 Graphic distribution format 20 Data validation 20 Appendix A.Standard DLG distribution format (record contents) 21 B.Optional DLG distribution format (record contents) 22 C.Graphic format 23 D.Map projection parameters 24 E.DLG attribute codes 25 F.Coordinate conversion 26 G.Sample DLG data file (standard distribution format) 27 H.Sample DLG data file (optional distribution format) 34 I.Data sources and currency 41 ILLUSTRATION- Page Figure l. Map elements showing roads, railroads, buildings, streams, lake and forest areas 7 2a. Pecos River, Southeastern New Mexico Scale 1:2,000,000 11 2b. Rivers and water bodies, New Mexico Scale 1:5,000,000 11 2c. Rivers and water bodies, New Mexico Scale 1:10,000,000 11 3. Sample line graph 12 2 4. Window from the Arizona-New Mexico, 1:2,000,000-scale sectional map of the National Atlas of the United States of America 14 5. Sample topology, Catron County, New Mexico 16 6. Multistate cells used for Digital Line Graphs from 1:2,000,000-scale maps 20 7. Location of origin of file reference coordinates 20 TABLES Page Table 1. Major codes used for DLG base categories 5 2. Description of the topological elements and relationships of a sample line graph 11 3. Selected sample of standard format DLG-3 records of Catron County, New Mexico [N, node; A, area; L, line] 15 4. Standard, optional, and graphic DLG format 18 DIGITAL LINE GRAPHS FROM 1:2,000,000-SCALE MAPS INTRODUCTION The Earth Science Information Centers (ESIC) distribute digital cartographic/geographic data files produced by the U.S. Geological Survey (USGS) as part of the National Mapping Program. Digital cartographic data files may be grouped into four basic types. The first of these, called a Digital Line Graph (DLG), is line map information in digital form. These data files include information on planimetric base categories, such as transportation, hydrography, and boundaries. The second type, called a Digital Elevation Model (DEM), consists of a sampled array of elevations for a number of ground positions that are usually at regularly spaced intervals. The third type is Land Use and Land Cover digital data, which provides information on nine major classes of land use such as urban, agricultural, or forest as well as associated map data such as political units and Federal land ownership. The fourth type, the Geographic Names Information System, provides primary information for all known places, features, and areas in the United States identified by a proper name. The digital cartographic data files from selected sources currently available from ESIC include the following: 3 Digital Line Graphs (DLG) --1:24,000-scale --1:62,500-scale --1:63,360-scale --1:100,000-scale --1:2,000,000-scale Digital Elevation Models (DEM) --7.5-minute --15-minute --30-minute --1-degree Land Use and Land Cover digital data --1:250,000- and 1:100,000-scale Land Use and Land Cover and associated maps --1:250,000-scale Alaska Interim Land Cover Geographic Names The digital data are useful for the production of cartographic products such as plotting base maps and for various kinds of spatial analysis. A major use of these digital cartographic/geographic data is to combine them with other geographically referenced data enabling scientists to conduct automated analyses in support of various decisionmaking processes. ----------------- Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Manuscript approved for publication September 4, 1986. ----------------- This document describes DLG's prepared from the 1:2,000,000-scale sectional maps (U.S. regions) of the National Atlas of the United States of America . DATA CONTENT The DLG data files derived from the 1:2,000,000-scale maps contain selected base categories of cartographic data in digital form. The data files are derived from the sectional maps of the 1970 National Atlas of the United States of America . The following categories are included in current 1:2,000,000-scale DLG files: Boundaries -- This category of data includes boundary information collected in two separate subcategories: (1) Political Boundaries and (2) Administrative Boundaries. Hydrography -- This category of data includes features collected in three separate subcategories: (1) Streams, (2) Water Bodies, and (3) Hypsography (Continental Divide only). 4 Transportation -- This category of data includes major transportation systems collected in three separate subcategories: (1) Roads and Trails, (2) Railroads, and (3) Cultural Features (airports and Alaska pipeline). DATA STRUCTURE Levels of Structuring The term DLG is employed by the USGS to describe a digital map data set in vector form. Originally, three levels of DLG data (DLG-1, DLG-2, and DLG-3) were proposed; these levels were differentiated by their positional accuracy, level of attribute coding, and relational spatial information. It was found, however, that the widest user-community would be served by producing DLG-3 data, which have the full range of attribute codes and are fully topologically structured. These two properties are required by users whose work includes both graphic and analytic applications. Therefore, all DLG data in the National Digital Cartographic Data Base are level 3 . Topology Data collection from 1:2,000,000-scale maps was exclusively directed toward producing fully topologically structured level-3 DLG data referred to as DLG-3. The DLG-3 concept is based on graph theory in which a two-dimensional diagram is expressed as a set of nodes (points in space) and links (line segments connecting nodes) in a manner that explicitly expresses logical relationships. Applied to a map, this concept is used to encode the digital data with the spatial relationships among map elements that are obvious when the map is examined visually. The spatial relationships include such concepts as adjacency and connectivity between features on the map. The abstraction of the map data according to the rules of graph theory preserves the spatial relationships inherent in the map graphic and creates a logical and consistent data file structure for computer processing. A digital file of cartographic or geographic data that maintains the spatial relationships inherent in the map is called a topologically structured data file. A topologically structured data file can support simple graphic applications, such as plotting streams and roads for base maps, as well as more advanced applications, such as computations involving areas and lines and their spatial relationships. 5 Topological Elements A DLG-3 file is composed of three separate, but related, types of elements: nodes, lines, and areas. Nodes define the location of the end-points of every line, and a single node may mark the start or end of one or more lines. Intersections of linear features and significant points on linear features are marked by nodes because at that point the linear feature is subdivided into line segments. A line is an ordered set of points that describes the position and shape of a linear feature on the map. Each line starts at a node and ends at a node and, thus, has both an explicit direction and a left-right connotation. The direction of the line is arbitrarily chosen at the time of digitizing. Lines connect to each other at nodes, and, by this definition, a line does not cross itself or any other line. A line may describe the boundary between two map features, such as counties, or may define a map feature by itself, such as a road. A special line, called a degenerate line, is used to define features symbolized as independent points on a map. A degenerate line starts and ends at the same node, has two identical coordinate pairs, has zero length, and is totally enclosed inside one map area. An area is a portion of the map bounded by lines. All portions of the map must be assigned to some area. Each area is identified in a DLG-3 data file by an arbitrary point chosen to represent the characteristics of the area; the point is not required to be inside the area it represents. Every DLG data file will have at least two areas identified: one representing the area covered by the file and the other representing the area outside the coverage of the file. Additional areas will be defined as necessary to subdivide the area covered by the file. Polygons as unique features are not defined explicitly in a standard DLG file. However, polygons can be constructed using line-area linkages built into the DLG data structure. ATTRIBUTE CODES In addition to locational and topological information, DLG data elements may have explicitly encoded attributes. Attribute codes, also called feature codes or classification attributes, are used to describe the map information represented by a node, area, or line. For example, the attribute code for an area might identify a lake or glacier; the attribute code for a line might identify a road, railroad, stream, or shoreline (fig. l). The codes are based on the cartographic features symbolized on the sectional maps of the 1970 National Atlas of the United States of America . 6 The map symbology of the source material used during digitizing and encoding of data elements has a strong influence on the overall classification strategy. A listing of all the attribute codes currently assigned and used in the 1:2,000,000-scale DLG files is given in Appendix E. Figure 1.--Map elements showing roads, railroads, buildings, streams, lake, and forest areas. Each attribute code identifies the major category to which a data element belongs, as well as the specific nature of the element. Codes also may provide additional descriptive information. Most elements are uniquely described by a single attribute code. Others, however, may require two or more codes for a complete description. If multiple attributes are needed to describe an element, the order is not significant. Allowing for a variable number of attribute codes creates an open-ended structure to which information may be added at any time. It is not necessary for each element to have associated attributes; in general, attribute codes are not assigned to an element if the attributes can be derived based on relationships to adjacent elements. In conventional DLG data files, features are described as they are symbolized or labeled on the source map. For the 1:2,000,000-scale data, however, additional information about the map features is included through a special attribute coding scheme. These codes not only describe the digitized features in a generic sense, but provide a means of selecting map features based on some indices of the significance of the features. These special attribute codes are provided to assist the user in selecting the features to be displayed on maps of various scales and themes. Because of the varying nature of the themes of data digitized, the indices of feature "significance" differs between data overlays. A DLG attribute code is composed of two distinct numeric fields: a three-digit major code, and a four-digit minor code. In the digital file, the major and minor attributes are encoded in two integer fields of six digits, flush right with leading blanks (FORTRAN 2I6 format). In this document, major codes are presented as three digits, and minor codes are presented as four digits. Leading zeros are shown for clarity; for example: 090 0104. Major Attribute Codes A list of the major codes and the categories they represent is contained in table 1. The first two digits of the major code (including leading zeroes) uniquely identify the category to which the described element belongs. The third digit of the major code is used to modify the minor code in two ways: 7 If zero, the minor code represents a description or classification of the element. If non-zero, the minor code which follows is a parameter requiring special interpretation according to instructions given in the codes for each category (see next section). Table 1.--Major codes used for DLG base categories Major Code Base Category 040 Water Bodies 090 Political and Administrative Boundaries 100 Transportation systems -- Roads and Trails 290 Special line attribute codes for 1:2,000,000-scale data NOTE:The coding scheme utilizing the major codes 040, 090, 100, and 290 applies only to 1:2,000,000-scale DLG data sets. The codes in the series 040, 090, and 100 are available only in the standard and optional DLG formats (described below). In the graphic data format, only the last two digits of the 290-code series are carried in the data. Minor Attribute Codes In the 1:2,000,000-scale data sets, two separate schemes are used to encode minor attribute codes: scheme one is used with the major code series 040, 090, and 100, and scheme two is used with major code series 290. These two schemes will be addressed separately. Scheme One: Minor Codes in the 040, 090, and 100 Series The codes in the 040 and 090 code series are used for area elements in the water body and boundary (both political and administrative) categories, respectively. The codes in the 100 code series are applied to the roads and trails category. If the third digit of the major code is zero, the minor code is interpreted to describe the file element in a generic sense (for example, as a lake, forest, or park). If the third digit of the major code is non-zero, the minor code is interpreted as identifying the file element representing part of a particular feature (for example, as the State of Virginia, Fairfax County, or Interstate 95). These codes are not included in the graphic data distribution format. 8 Examples of these attribute codes include: 040 0100 The major code 040 indicates the water body category. The minor code 0100 identifies the feature as a perennial lake or pond. 090 0104 The major code 090 indicates one of the boundary categories. The minor code 0104 identifies the feature as a national forest or grassland. 091 0051 The major code 091 indicates a State in the boundary 092 0059 category. Because the last digit of the major code is non-zero, the minor code is a parameter. The minor code 0051 is the Federal Information Processing Standards (FIPS) code for the State of Virginia. Similarly, the major code 092 indicates a county in the boundary category. The minor code 0059 is the FIPS code for Fairfax County. 102 0095 The major code 102 indicates an interstate highway in the roads and trails category. Because the last digit of the major code is non-zero, the minor code is interpreted as a parameter code. The minor code 0095 indicates that the element with which this code is associated is part of Interstate 95. Scheme Two: Minor Codes in the 290 Series During the planning of the 1:2,000,000-scale data sets, it was decided that the data should support the generation of a variety of maps of different scales and themes. During the process of making different maps, it is necessary to change the amount of data displayed to support the theme or scale of the map. One of these changes is to control the selection of features to be displayed based on some indices of significance or importance. The 290-code series represents an attempt to encode selected indices of significance or importance in the data. By careful selection of features through the use of these attribute codes, one can control the amount of information displayed. The minor codes in the 290 series are composed of four digits. The first digit indicates the category of data. The second digit is always zero. The last two digits both identify the feature in a generic sense and contain some index of significance. A description of the minor codes for each numeric series follows: 2000-2099: Hypsography. The only feature currently stored is the Continental Divide. 3000-3099: Streams. Examples of the features encoded include perennial, intermittent, and braided streams, and canals. In addition to the generic description, each feature is further categorized based on an approximate measure of overall feature length. In estimating the length of a feature, the path of a stream was determined by following the named (labeled) channel as far as possible, and then following the longest tributary. 9 4000-4099: Water Bodies. Examples of these features include perennial, intermittent, and dry lakes. Each feature is further classified by length along the longest dimension of the feature. 5000-5069: Roads and Trails. Examples of these features include Interstate, U.S., and State highways. Each feature is further classified by such characteristics as length, access type (limited or non-limited access), proximity to a parallel route of a higher class, and as serving as a connector in a network of highways of a higher class. 5070-5080: Railroads. Railroads are classified based on a U.S. Department of Transportation classification scheme. 6000-6019: Political Boundaries. Classification is based on a hierarchical scheme of national, State, and county boundaries. Maritime boundary areas are usually closed by unattributed arbitrary extension lines and do not follow the shoreline. 6020-6099: Administrative Boundaries. Examples of these features include national parks, forests, wilderness areas, and Indian reservations. Each feature is further classified by length along the longest dimension of the feature. 7000-7099: Cultural Features (also referred to as Miscellaneous Transportation). Includes civilian and military airports and the Alaskan pipeline. Airports are only available in the standard and optional data distribution formats (refer to the Distribution format section). An example of the use of these codes to control feature selection is illustrated in figures 2a through c. A map produced at a scale of 1:2,000,000 might include all streams from feature codes 3003 through 3016 and 3008 through 3030 (fig. 2a). A map at a scale of 1:5,000,000 might include streams with a length of greater than 50 kilometers (using feature codes 3007 through 3016 and 3021 through 3030) (fig. 2b). Finally, at a scale of 1:10,000,000, a map might only display those features with a length greater than 100 kilometers (using codes 3010 through 3016 and 3024 through 3030) (fig. 2c). These figures also illustrate the use of the "centerline in water body" codes (3035 through 3059). In generating a graphic of drainage for an area, normally data from both the stream and water body overlays is portrayed. When controlling the number of water bodies displayed in a graphic, it is possible that gaps will appear in a stream network where small bodies of water were not selected for display. The "centerline in water body" codes were meant to fill these gaps. For example, the codes were designed so that, if perennial lakes of length of 2 to less than 4 kilometers (code 4002) were not selected for display, the centerline in perennial lakes of 2 to less than 4 kilometers (code 3036) would be selected to maintain connectivity in the stream network. 10 Unfortunately, these centerline codes only reference the body of water in which they reside and not the stream to which they are connected. It is possible that centerlines might be requested for display and the stream to which they connect not be selected for display. SAMPLE LINE GRAPH STRUCTURE Examples of a line graph and its corresponding digital records are given in figure 3 and table 2. These examples are simplified representations of the concepts used in the DLG-3 structure; they are not actual data files. The example shown is composed of 13 nodes, labeled N1 through N13, 5 areas, labeled A1 through A5, and 15 lines, labeled L1 through L15. Each element type is maintained as a separate list in the digital data. Figure 2a.--Pecos River, southeastern New Mexico. Scale: 1:2,000,000. The map represented by the example is divided into five distinct areas. Area Al represents the area outside of the map border. There is one outside area for each DLG-3. It is always the first area encountered and has the attribute code 000 0000. In the example given in figure 3, the portion of the map inside the border is divided into four areas, each bounded (closed) by lines. Area A2 is bounded by lines Ll4, Ll, L4, and L5. Area A3 is bounded by lines L3, Ll3, L4, L6, L7, L8, L15, and L9. Area A4 is bounded by lines L8, L15, and L9. Area A5 is bounded by lines L5, L6, L7, and Ll0 and L2. Figure 2b.--Rivers and water bodies, New Mexico. Scale: 1:5,000,000. Figure 2c.--Rivers and water bodies, New Mexico. Scale: 1:10,000,000. In this example, line elements contain the only explicit topological references. Each line contains pointers to its bounding nodes (starting and ending) and the areas that it bounds (left and right of the line). This format is similar in concept to the standard DLG-3 data structure, which minimizes redundant linkages to achieve efficient data encoding and storage. The lines in figure 3 are labeled L1 through L15. The lines can be identified by their starting node number, ending node number, number of the area to the left of the direction of travel, number of the area to the right of the direction of travel, and string of coordinates describing the alignment of the line. 11 In this example, only two pairs of coordinates are shown; however, in an actual file, an irregular line would have a variable number of coordinate pairs up to a limit of 1,500 coordinate pairs. The direction of travel of the line is arbitrarily determined during the digitizing operation. In this example, L1 is encoded as proceeding clockwise around area A2. Thus line L1 starts at node N1, ends at node N3, has area A1 to the left of the direction of travel, and has area A2 to the right of the direction of travel. The coordinate string describing the alignment of the line will start with the same coordinate values as that of node N1 and will end with the same coordinate values as that of node N3. Because the area to the left of its direction of travel, A1, is different from the area to the right of its direction of travel, A2, the line is known to be a boundary between the two areas. Figure 3.--Sample line graph. Table 2.--Description of the topological elements and relationships of a sample line graph (see fig. 3) Nodes Areas Internal Internal Id Id Number X Coordinate Y Coordinate Number X Coordinate Y Coordinate N1 1 28 A1 0 0 N2 13 14 A2 6 24 N3 23 28 A3 3 10 N4 13 1 A4 8 7 N5 13 7 A5 18 14 N6 22 10 N7 6 5 N8 10 4 N9 11 24 N10 23 1 N11 1 17 N12 1 1 N13 9 9 _________________________________________________________________ 12 Lines _________________________________________________________________ Nodes Area Coordinates Number Starting Ending Left Right (first x y last x y) L1 1 3 1 2 1, 28 23, 28 L2 3 10 1 5 23, 28 23, 1 L3 4 12 1 3 13, 1 1, 1 L4 11 2 2 3 1, 17 .... 13, 14 L5 2 3 2 5 13, 14 23, 28 L6 2 5 5 3 13, 14 13, 7 L7 5 4 5 3 13, 7 13, 1 L8 13 7 4 3 9, 9 .... 6, 5 L9 7 8 4 3 6, 5 .... 10, 4 L10 4 10 5 1 13, 1 23, 1 L11 5 6 5 5 13, 7 .... 22, 10 L12 9 9 2 2 11, 24 11, 24 L13 12 11 1 3 1, 1 1, 17 L14 11 1 1 2 1, 17 1, 28 L15 8 13 4 3 10, 4 .... 9, 9 Lines L11 and L12 are examples of lines that lie within one area. In this example, line L11 starts at node N5, ends at node N6, has area A5 to the left of the direction of travel, and again has area A5 to the right of the direction of travel. The coordinate string for the line will start with the same coordinate values as that of node N5 and will end with the same coordinate value as that of node N6. Line L12 is an example of a degenerate line. The line starts at node N9, ends at node N9, and has area A2 as both the area to its left and right. There are only two coordinate pairs in the string defining the line: both points have the same coordinate values as node N9; thus, the two points are the same and the line has zero length. The line graph concept allows all of the points on the map to be described as a member of a line graph element (node, area, or line) with minimal redundancy. The relationships between the various elements are indicated by the structure. Note that in this example the x and y coordinates are numbered from the lower left corner to simplify the drawing. In an actual DLG-3 file, the origin is the center of the map and the internal file coordinates are numbered plus or minus 1 to 32,767 expressed in thousandths of inches. See the section labeled "Coordinate Systems" for more detail. GRAPH THEORY IN DLG DATA There are two ways to implement the line graph concept in DLG files: the area case and the network case. These cases are differentiated by the nature of the information contained in the categories. 13 Area line graphs are used to represent areal features such as political entities or water bodies. Area line graphs correspond directly to the general line graph case in that each closed area on the map is represented by a distinct area element. Data categories that are collected as area line graphs include: Political Boundaries Administrative Boundaries Water Bodies Network line graphs are used to represent linear features in digital form. The network case differs from the area case in that, irrespective of the number of closed areas forming the graph, only two area elements are encoded: (1) the area outside the graph, termed the outside area; and (2) the area within the graph, termed the background area. All lines except the graph boundary are considered to be contained within the background area. The major topological relationship expressed by network data is that of connectivity. Data encoded in network line graph form are suitable for various forms of network analysis, such as minimum path computations. Data categories that can be collected as network line graphs include: Roads and Trails Railroads Cultural Features Streams Hypsography (Continental Divide only) In the area case, such as the boundary data collected from 1:2,000,000-scale maps, all areas on the graph have an identity pertinent to the category and are assigned attribute codes to describe them. The lines in such cases derive their significance from the areas they border. In the network case, as implemented in roads and trails collected from 1:2,000,000-scale maps, the lines themselves have the identity and are assigned attribute codes to describe them. The background area, represented by a single area record, does not have an attribute code assigned to it. Figure 4 shows a window in the vicinity of Catron County, New Mexico, taken from the Arizona and New Mexico 1:2,000,000-scale map. Figure 5 shows the line graph encoded for the boundaries of the same area. Certain nodes, areas, and lines are labeled. Table 3 contains some of the digital data records extracted from the node, area, and line lists which describe this portion of the graph. (Note: Descriptions of DLG-3 formats are contained in Appendixes A, B, and C, and a list of attribute codes is contained in Appendix E.) In the example, each node and area element is described by one or two logical records: (1) a type D.1 record that describes the element, and (2) an optional type F record that lists the attribute codes associated with the element. 14 The first record (type D.1) for each node and area element contains the following fields: 1. Type of record indicator, N for node or A for area. 2. Internal sequence identification number. 3. x coordinate of node or representative area point. 4. y coordinate of node or representative area point. 5. Number of attribute codes that describe the element. 6. Number of pairs of characters in the text string that describes the element. The second record (type F) for each node and area element contains n attribute codes (expressed as major and minor code pairs), where n is the number specified in field 5 of the first (type D.1) record. Each line element in the example is described by two or three logical records: (1) a type D.2 line description record, and (2) a type E record that lists the x,y coordinate pairs that define the shape of the line, and, if appropriate, (3) a type F (attribute code) record. The first record (type D.2) for each line element contains the following fields: 1. Type of record indicator (L). 2. Internal sequence identification number. 3. Internal sequence number of starting node. 4. Internal sequence number of ending node. 5. Internal sequence number of the area to the left of the line. 6. Internal sequence number of the area to the right of the line. 7. Number of x,y coordinate pairs that locate the line on the map. 8. Number of attribute codes that describe the line. 9. Number of pairs of characters in the text string that describes the line. The second logical record (type E) for each line element contains n coordinate pairs, where n is the number specified in field 7 of the first (type D.2) record. The type F record is as described above. The topological pointers contained in the DLG-3 line elements enable a user to manipulate the data based on the spatial relationships. For example, some applications require areal data to be expressed as closed strings of x,y coordinate pairs. For such applications the user can request that the data be supplied in the optional distribution format. In this format the references to the boundary lines of each area are explicitly coded into the area record. For other applications the standard format may be preferable. Figure 4.--Window from the Arizona-New Mexico, 1:2,000,000-scale sectional map of the National Atlas of the United States of America . 15 The specific records in table 3 describe Catron County, New Mexico. The county is described by 6 nodes, 1 area, and 6 lines. The area information, encoded in area record 10, includes the position of the area record (428, -934) and the attribute codes 091 0035 and 092 0003 identifying the area as being in the State of New Mexico and Catron County respectively. The boundary of the county is formed by lines 76, 79, 80, 85, 86, and 87. They can be verified as forming the boundary of this area by noting that each line has area 10 as the area to the left or right of the direction in which the line was digitized. In addition, the lines have attribute codes identifying them as portions of State boundaries (code 290 6005) or county boundaries (290 6009). The lines may be connected to form a closed loop around the area. This may be accomplished by reordering the line elements in a clockwise direction (where area 10 is always to the right of the direction of travel) or in a counterclockwise direction (where area 10 is always to the left of the direction of travel). (In reordering the direction of a line element, the starting node becomes the ending node (and vice versa), the area left becomes the area right (and vice versa), and the points describing the line are reordered (the first point becomes the last point, the second point becomes the second to the last point, etc.).) Once the lines are ordered correctly, the lines may be connected by using the starting and ending node information. Island-like features must be handled separately. Users whose applications will require this sort of structure should consider purchasing the optional format of the DLG data, which contains these forward and inverse pointers between lines and area and line and nodes. Figure 5.--Sample topology, Catron County, New Mexico. Table 3.--Selected sample of standard format DLG-3 records of Catron County, New Mexico [N, node; A, area; L, line] N 44 -86 948 0 0 N 45 -90 -831 0 0 . . . N 52 2297 947 0 0 N 53 2361 -1484 0 0 . . . N 56 1840 -2085 0 0 . . . N 115 -91 -2102 0 0 . . . 16 A 10 428 -934 2 0 91 35 92 3 . . . L 76 44 52 l2 10 4 1 0 -86 948 1155 938 1565 940 2297 947 290 6009 . . . L 79 115 45 29 10 3 1 0 -91 -2102 -91 -1770 -90 -831 290 6005 L 80 45 44 30 l0 3 1 0 -90 -831 -86 8 -86 948 290 6005 . . . L 85 53 52 10 9 4 1 0 2361 -1484 2329 -706 2319 252 2297 947 290 6009 L 86 115 56 10 7 3 1 0 -91 2102 195 -2091 1840 -2085 290 6009 L 87 56 53 10 6 4 1 0 1840 -2085 1842 -1482 2285 -1484 2361 -1484 290 6009 DISTRIBUTION FORMATS The 1:2,000,000-scale DLG data are available in three distribution formats: (1) standard, (2) optional, and (3) graphic. The standard distribution format was designed to minimize storage requirements. Explicit topological linkages are contained only in the line elements. A sample DLG data file in standard format is illustrated in Appendix G. The optional distribution format was designed for data interchange. These files are typically larger than those in the standard format but, for certain applications, can simplify processing requirements. Topological linkages are explicitly encoded between all line and node elements, and all line and area elements. This structure allows a polygon data structure to be easily created. A sample DLG data file in optional format is illustrated in Appendix H. 17 The graphic distribution format was designed to be compatible with the GS-CAM (Geological Survey - Cartographic Automatic Mapping) software. This software provides for plotting line and point information using a variety of map projections, scales, and graphic symbologies. To obtain information on the availability of the GS-CAM software, please refer to the inside front cover of this publication. The files in the graphic distribution format are derived from the topologically structured DLG data described above, and contain a subset of the line and attribute code information in the DLG files. No node or area information is stored in these files. These files are not topologically structured. The characteristics of the standard, optional, and graphic DLG formats are summarized in table 4. Table 4.--Standard, optional, and graphic DLG format Standard Optional Graphic Character set 8-bit ASCII 8-bit ASCII 8-bit ASCII Logical record length 144 bytes 80 bytes 20 bytes Physical record variable in variable in variable in length (blocksize) multiples of multiples of multiples 144 bytes 80 bytes of 20 bytes Coordinate system internal file ground geographic (thousandths of planimetric (latitude a map inch) (Albers and longitude) Equal-Area Conic) Topological contained only contained in none (only linkages in line elements node, area, and contains line elements line elements) These formats are described in detail in Appendixes A, B, and C. SOURCE MATERIALS The data described in this document are derived from USGS 1:2,000,000-scale reference maps from The National Atlas of the United States of America . Selective updating of the maps was done prior to digitizing. Data source and currency information may be found in Appendix I. 18 The data for the conterminous United States and Hawaii were collected from 1:2,000,000-scale map manuscripts. For Alaska, the boundary and transportation data were digitized from 1:2,000,000- scale source documents; the hydrographic data were digitized from 1:1,000,000-scale source documents. The scale of the source materials used to generate a DLG is contained in the file header. The scale is also reflected in the resolution field, which states the ground length in meters of the smallest data collection unit 0.001 inch (50.8 meters for 1:2,000,000-scale data; 25.4 meters for 1:1,000,000-scale data). CELL SIZE AND FILE EXTENT The DLG's are distributed predominantly in multistate cells (fig. 6). There are a total of 21 cells for the United States: 15 for the conterminous United States, 5 for Alaska, and 1 for Hawaii. In general, States are not divided between cells. Three States (California, Texas, and Montana) are divided between two cells along county boundaries. Alaska is divided among five cells along arcs of longitude and/or latitude. The data for each cell are encoded in multiple thematic categories (Political Boundaries, Administrative Boundaries, Roads and Trails, Railroads, Cultural Features, Streams, Water Bodies, and (where appropriate) Hypsography). Normally, there is one file per category. Due to software limitations at the time of digitizing, however, some categories with a large number of elements may be encoded in several files. Files are not horizontally integrated (edge joined) between cells. COORDINATE SYSTEMS The positional descriptions for DLG data elements are expressed in one of three coordinate systems, dependent upon the distribution format selected. These distribution formats - standard, optional, and graphic - are described below. Standard Distribution Format The DLG data in the standard distribution format are encoded using an internal file coordinate system to minimize storage requirements. The characteristics of this system are as follows: 1. The coordinate system is Cartesian. 2. The origin (x=0, y=0) is at the center of the cell (fig. 7). 3. The x-axis of the coordinate system is parallel to a theoretical straight line connecting the southwest and southeast registration points of the cell, y-axis is perpendicular to that line. 4. One unit is equal to 0.00l-inch at map scale. 5. The coordinate domain is limited to the range -32768 to +32767. 19 Figure 6.--Multistate cells used for Digital Line Graphs from 1:2,000,000-scale maps. Figure 7.--Location of origin of file reference coordinates. The file header contains the parameters of a transformation which can be used to convert the internal file coordinates to the ground coordinate system, which is the Albers Equal-Area Conic Projection for 1:2,000,000-scale DLG's. An example of this transformation is given in Appendix F. Optional Distribution Format The DLG data in the optional distribution format are expressed in the units of the ground coordinate system, that is, meters in the Albers Equal-Area Conic coordinate systems described in Appendix D. Graphic Distribution Format The data in the graphic distribution format are expressed in geographic coordinates (latitude- longitude). These values are expressed in degrees-minutes- seconds. DATA VALIDATION The DLG data do not currently carry quantified accuracy statements. The following procedures, however, are used to validate the data files before they are released for distribution: 1. File fidelity and completeness -- The data are manually digitized using equipment with a resolution of 0.00l inch and an absolute accuracy of from 0.003 to 0.005 inch. The positional accuracy of the data and completeness of the file are checked by visually comparing proof plots with the original stable-base source material. These proof plots are generated using automated drafting machines with a resolution of 0.00l inch and an absolute accuracy of from 0.003 to 0.005 inch. 2. Attribute accuracy -- Validating the codes for correct application is currently a manual process involving the correlation of formatted listings with proof plots. 20 3. Topological fidelity -- The topological structure of each DLG file is fully validated by software. There are no extraneous intersections; that is, a line does not join or cross another line, or itself, except at a node. No line extends through a node. Polygon (area) adjacency is also validated; that is, area left and right topological attributes of lines are consistent throughout the file. The neatline is free of gaps. Validation of DLG data is performed for each category within a file. [Note: A deficiency in the topological validation software was discovered after the data were processed. For some graphic representations the software did not check the topology of island-like features correctly; some features of this type may have incorrect topology in the files.] APPENDIXES APPENDIX A.--Standard DLG Distribution Format (Record Contents) In the standard DLG distribution format, the topological linkages are contained only in the line elements. The files are physically comprised of standard 8-bit ASCII characters organized into fixed-length logical records of l44 characters. Nine distinct record types are defined. Logical record type Content A Header record containing DLG identification information. B Header record containing projection information and registration points. C Header record identifying data categories contained in this DLG and indicating the number of nodes, areas, and lines in each category. D.l A node or an area record. D.2 A line record. E Record containing x,y coordinate string. F Record containing attribute codes. G Record containing text string (not currently used). H Accuracy estimate (not currently used). The actual sequence of records in a standard distribution DLG file is as follows: l. Header records Type A (one record) Type B (one record) Type C (one record) 21 2. Data records Node records Repeated Node description (D.l) for each Attribute codes (F) node within a Text string (G) data category Area records Area description (D.l) Repeated Repeated Attribute codes (F) for each for each Text string (G) area within a data category data category Line records Line description (D.2) Repeated x,y coordinates (E) for each Attribute codes (F) line within a Text string (G) data category 3. Accuracy estimate Type H (one record) (not currently used) Descriptions of the contents of records A-F are contained in the following tables. The tables also reflect the relationship between these record types and l44-byte logical records. APPENDIX B.--Optional DLG Distribution Format (Record Contents) In the optional DLG distribution format, topological linkages are explicitly encoded for node and area elements as well as for line elements. The files are physically comprised of 8-bit ASCII characters organized into fixed-length logical records of 80 characters (bytes). Bytes 1-72 of each record may contain DLG data, and bytes 73-80 may contain a record sequence number. The 11 distinct record types used in the optional DLG distribution format may be categorized as header and data records. Four types of records are considered header records: File identification and description records Accuracy records (not currently used) Control-point identification records Data-category identification records Seven types of records are considered data records: Node and area identification records Node-to-line linkage records Area-to-line linkage records 22 Line identification records (also contains line-to-node and line-to-area linkages) Coordinate string records Attribute code records Text records (not currently used) The actual sequence of records in an optional distribution format DLG file is as follows: l. Header records Ten file identification and description records Accuracy records (not currently used) Control point identification records (one per control-point) Data category identification records (one per data category in the file) 2. Data records Node identification record Repeated Node-to-line linkage record(s) for each Attribute code record(s) node within a Text record(s) data category Area identification record Repeated Repeated Area-to-line linkage record(s) for each for each Attribute code record(s) area within a data category Text record(s) data category Line identification records Repeated Coordinate string record(s) for each Attribute code record(s) line within a Text record(s) data category Descriptions of the contents of the various types of records in an optional distribution format DLG are contained in the following tables. APPENDIX C.--Graphic Format The simplified, graphic format that can be used with the GS-CAM plotting package is described below. In this format, each line record from the DLG format has been reformatted into two record types: one line identifier record and multiple latitude- longitude records (one for each coordinate pair). Supplementary coordinate pairs have been added to Graphic Format data in instances where the distance between two adjacent vertices was greater than 0.01" in the original DLG line description. These additional points assure that the distance between any two data points of a line are no greater than 0.01" and minimizes distortion of the line when projection transformations are applied. If a line record has more than one attribute code associated with it in the DLG format, that line record appears in the graphic format files multiple times (once for each attribute code). The graphic format files are organized by feature type. 23 Record 1: Line identifier record Position Length Format 1. Line identifier 1-7 7 I7 2. Rank (last two digits of attribute code 8-9 2 I2 (described in Appendix E--unique within category) 3. Number of points in the line (NP) 10-15 6 I6 (latitude and longitude) 4. First five digits of attribute code 16-20 5 I5 (described in Appendix E) Record 2: Latitude-longitude record (repeated NP times) 1. Latitude (DDMMSSI) 1-7 7 3I2, Al 2. Longitude (DDDMMSSI) 8-15 8 I3, 2I2, Al 3. Sequence count 16-20 5 I5 APPENDIX D.--Map Projection Parameters Albers Equal-Area Conic Projection The standard and optional DLG distribution formats include 15 fields reserved for map projection parameters. These parameters are typically used as input for a coordinate transformation package such as the USGS General Coordinate Transformation Package (GCTP). When the ground coordinate system of a DLG is the Albers Equal- Area Conic projection, as in the case for all DLG's digitized from 1:2,000,000-scale maps, the first eight parameter fields are used: 1. Semimajor axis of ellipsoid 2. Eccentricity squared of ellipsoid 3. Latitude of first standard parallel 4. Latitude of second standard parallel 5. Longitude of central meridian 6. Latitude of projection origin 7. False easting 8. False northing 9-15. Not used For the 1:2,000,000-scale files, the following parameters were used: For all maps: Spheroid parameters: Clarke 1866 False easting: 0.0 False northing: 0.0 24 For conterminous United States: First standard parallel: 29.5 North Second standard parallel: 45.5 North Longitude of central meridian: 96 West Latitude of projection origin: 23 North For Hawaii: First standard parallel: 8 North Second standard parallel: 18 North Longitude of central meridian: 157 West Latitude of projection origin: 3 North For Alaska: First standard parallel: 55 North Second standard parallel: 65 North Longitude of central meridian: 154 West Latitude of projection origin: 50 North A transformation to or from Albers Equal-Area Conic projection coordinates using GCTP can be controlled by specifying the parameters stated above. In the projection parameters of a DLG file, the longitude-latitude parameter values are encoded as packed, degrees-minutes-seconds (DMS) as follows: degrees * 1000000 + minutes * 1000 + seconds For example, if degrees = +50, minutes = 30, and seconds = 36.25, then the parameter value is 50030036.25 stored as a REAL*8 variable, and "bbb0.500300362500000D 08" encoded in FORTRAN D24.15 format. APPENDIX F.--Coordinate Conversion This appendix illustrates the procedure for converting internal file coordinates to ground planimetric reference coordinates. The formulas for this conversion are as follows: X=A1x+A2y+A3 Y=A1y-A2x+A4 where X and Y are the ground planimetric coordinate values and x and y are the internal file coordinates. The parameters for these formulas (A1, A2, A3, and A4) are contained in Header Record B, as double- precision floating-point numbers. 25 This example converts four coordinate pairs from internal file coordinates to ground planimetric coordinate values (Albers Equal-Area Conic projection). The parameters are as follows: A1= 50.325538142 A2= 6.9275199981 A3= -1185878.9723 A4= 1314164.3401 The internal file coordinates to be converted are: x y 1st pair -11238 -6583 2d pair -10405 6583 3d pair 10405 6583 4th pair 11238 -6583 The calculation to determine the ground planimteric coordinates for the first pair are as follows: X=(50.325538142)(-11238)+(6.9275199981)(-6583)+(-1185878.9723) =-1797041.23 Y=(50.325538142)(-6583)-(6.927519998l)(-11238)+(1314164.3401) =1060722.79 The resulting x,y coordinate values for the four pairs given above are as follows: 1st pair -1,797,041.23 1,060,722.79 2d pair -1,663,912.33 1,717,538.20 3d pair -6l6,637.88 1,573,376.51 4th pair -665,924.44 905,019.86 APPENDIX G.--Sample DLG data file (Standard Distribution Format) ARIZONA AND NEW MEXICO 1967, 1972 2000000. 3 3 9999 0.637820640000000D+07 0.676865799729109D- 02 0.2 90300000000000D+08 0.450300000000000D+08 - 0.960000000000000D+08 0.230000000000000D+08 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2 0.508000000000000D+02 0 4 -0.115000000000000D+03 0.310000000000000D+02 - 26 0.115000000000000D+03 0.370000000000000D+02 -0.103000000000000D+03 0.370000000000000D+02 -0.103000000000000D+03 0.310000000000000D+02 0.503255381420000D+02 0.692751999810000D+01 - 0.118587897230000D+07 0.131416434010000D+07 4 SW-11238 -6583NW-10405 6583NE 10405 6583SE 11238 -6583 1 HYPSOGRAPHY 795 18 795 2 530 13 N 1-11238 -6583 0 0 N 2-10405 6583 0 0 N 3 10405 6583 0 0 N 4 11238 -6583 0 0 N 5 1115 -3388 0 0 N 6 465 -6194 0 0 N 7 1307 -1163 0 0 N 8 932 1388 0 0 N 9 3513 4531 0 0 N 10 4036 6283 0 0 N 11 1 -6187 0 0 N 12 10635 2183 0 0 N 13 5207 6274 0 0 N 14 7 6246 0 0 APPENDIX G.--Sample DLG data file (Standard Distribution Format)--continued N 15 -5201 6334 0 0 N 16-10031 3973 0 0 N 17-10023 -857 0 0 N 18 10402 6519 0 0 27 A 1 -96 5417 1 0 0 0 A 2 287 3013 0 0 L 1 5 6 2 2 334 1 0 1115 -3388 1102 -3399 1096 -3411 1090 -3423 1083 -3428 1075 -3434 1067 -3444 1062 -3463 1062 -3480 1063 -3490 1062 -3497 1056 -3504 1051 -3507 1046 -3512 1041 -3522 1038 -3530 1035 -3539 1033 -3544 1030 -3549 1025 -3549 1017 -3549 1007 -3554 996 -3563 991 -3567 986 -3570 982 -3572 979 -3578 977 -3585 977 -3594 976 -3600 973 -3607 972 -3614 973 -3619 980 -3626 987 -3632 997 -3646 1015 -3660 1035 -3674 1064 -3687 1089 -3701 1111 -3714 1142 -3730 1191 -3767 1208 -3783 1232 -3810 1274 -3885 1279 -3913 1288 -3941 1290 -3969 1288 -3982 1286 -4001 1287 -4015 1287 -4030 1288 -4041 1287 -4055 1285 -4070 1285 -4085 1286 -4106 1284 -4120 1288 -4132 1285 -4146 1283 -4162 1281 -4176 1278 -4187 1280 -4200 1285 -4223 1291 -4231 1296 -4236 1300 -4244 1309 -4262 1325 -4283 1352 -4308 1375 -4337 1396 -4363 1421 -4382 1450 -4410 1477 -4434 1496 -4450 1501 -4457 1510 -4472 1513 -4483 1518 -4492 1521 -4503 1531 -4527 1543 -4560 1550 -4595 1547 -4616 1538 -4631 1528 -4647 1510 -4658 1494 -4666 1487 -4671 1479 -4686 1475 -4693 1469 -4705 1462 -4721 1458 -4729 1449 -4738 1442 -4745 1429 -4751 1417 -4759 1401 -4762 1386 -4764 1374 -4764 1360 -4765 1344 -4764 1325 -4762 1309 -4763 1296 -4760 1286 -4759 1278 -4763 1267 -4764 1254 -4768 1231 -4780 1206 -4790 1187 -4797 1174 -4803 1162 -4809 1149 -4816 1134 -4821 1127 -4824 1121 -4831 1110 -4835 1098 -4839 1089 -4842 1079 -4839 1071 -4834 1060 -4825 1055 -4817 1050 -4799 1040 -4784 1029 -4770 1021 -4760 1006 -4744 992 -4727 972 -4710 949 -4690 939 -4678 28 930 -4665 925 -4652 923 -4640 920 -4627 911 -4605 910 -4594 903 -4578 899 -4568 891 -4561 880 -4552 870 -4545 859 -4538 846 -4536 837 -4535 827 -4534 816 -4538 804 -4539 793 -4537 290 2017 L 2 5 7 2 2 364 1 0 APPENDIX G.--Sample DLG data file (Standard Distribution Format)--continued 1115 -3388 1124 -3380 1131 -3377 1142 -3376 1147 -3376 1150 -3374 1157 -3369 1163 -3361 1168 -3353 1170 -3346 1172 -3336 1174 -3328 1176 -3323 1181 -3320 1188 -3317 1198 -3312 1204 -3310 1210 -3306 1215 -3301 1218 -3294 1217 -3283 1213 -3269 1212 -3255 1206 -3240 1197 -3219 1194 -3204 1195 -3197 1196 -3186 1197 -3176 1204 -3166 1211 -3152 1218 -3138 1230 -3128 1237 -3116 1244 -3101 1248 -3090 1250 -3084 1249 -3073 1246 -3063 1239 -3045 1237 -3042 1238 -3034 1246 -3020 1250 -3005 1251 -2994 1250 -2985 1251 -2977 1247 -2973 1241 -2964 1231 -2960 1225 -2952 1216 -2940 1212 -2933 1208 -2928 1195 -2910 1192 -2900 1188 -2892 1192 -2890 1201 -2890 1211 -2892 1163 290 2017 L 3 9 8 2 2 461 1 0 3513 4531 3504 4525 3494 4520 3488 4515 3482 4506 3473 4497 3468 4480 3464 4470 3460 4462 3457 4451 3454 4439 3451 4432 3446 4419 3443 4401 3436 4378 3431 4366 3426 4356 3421 4344 3405 4336 3379 4331 3362 4326 3340 4317 3330 4309 3316 4300 3309 4290 3303 4279 3290 4265 3285 4259 3276 4246 3266 4232 3248 4225 3239 4222 3225 4217 3212 4215 3191 4215 3173 4218 29 3155 4221 3133 4223 3124 4220 3108 4213 3093 4208 3075 4207 3057 4208 3035 4209 3018 4210 2993 4209 2969 4206 2954 4197 932 1388 290 2017 L 4 10 9 2 2 229 1 0 4036 6283 4028 6280 4022 6276 4012 6271 4005 6269 3995 6270 3987 6270 3975 6274 3970 6272 3965 6267 3960 6258 3960 6252 3962 6242 3965 6227 3961 6224 3955 6221 3947 6216 3953 6213 3962 6207 3969 6201 3979 6193 3981 6188 3982 6180 3986 6172 3990 6160 3993 6155 3996 6148 4004 6137 4005 6125 4006 6111 4007 6106 4010 6098 4011 6090 4008 6089 4003 6087 3998 6084 3990 6078 3984 6074 3980 6067 3976 6065 3970 6063 3950 6054 3939 6047 3932 6046 3922 6035 3916 6028 3906 6015 3899 6009 290 2017 L 5 12 6 1 2 125 0 0 10635 2183 10658 1872 10668 1729 10679 1579 10688 1469 10688 1379 10682 1310 10690 1197 10702 1047 10710 888 10716 821 10720 732 10735 533 10746 337 10764 37 10786 -390 10794 -568 10801 -786 APPENDIX G.--Sample DLG data file (Standard Distribution Format)--continued 10810 -944 10820 -1133 10822 -1307 10828 -1399 10834 -1499 10847 -1778 10859 -1986 10869 -2186 10877 -2330 10892 -2527 10904 -2707 10918 -2953 10934 -3208 10944 -3383 10958 -3621 10974 -3868 10988 -4085 11002 -4334 11005 -4403 10401 -4442 9737 -4473 9539 -4480 9366 -4489 9237 -4498 9146 -4505 9066 -4509 8895 -4520 8761 -4530 8562 -4535 8432 -4540 8242 -4546 8019 -4555 7920 -4556 7853 -4557 7806 -4561 7732 -4570 30 7670 -4572 7607 -4575 7531 -4580 7402 -4587 7294 -4591 7151 -4598 6944 -4608 6706 -4614 6393 -4625 6222 -4630 5917 -4644 5728 -4650 5477 -4661 5086 -4668 4689 -4680 4431 -4683 4412 -4691 4400 -4702 4376 -4719 4372 -4722 4370 -4733 4373 -4744 4390 -4753 4404 -4753 4417 -4760 4414 -4786 4406 -4796 4401 -4813 4402 -4837 4403 -4856 4404 -4865 4403 -4879 4395 -4886 4388 -4890 4384 -4894 4384 -4907 4395 -4927 4399 -4936 4410 -4946 4418 -4964 4424 -4978 4421 -4992 4412 -4999 4410 -5002 4421 -5019 4434 -5027 4438 -5050 4448 -5075 4452 -5084 4455 -5088 4470 -5093 4478 -5097 4490 -5103 4500 -5108 4506 -5113 4527 -5120 4544 -5124 4563 -5130 4569 -5133 4579 -5143 4587 -5159 4227 -5162 3593 -5182 3138 -5195 2577 -5202 2122 -5206 1622 -5212 1471 -5212 1473 -6186 881 -6190 465 -6194 L 6 6 11 1 2 3 0 0 465 -6194 176 -6193 1 -6187 L 7 15 14 1 2 16 0 0 -5201 6334 -4824 6327 -4194 6312 -3442 6299 -2851 6288 - 2609 6286 -2587 6283 -2578 6281 -2560 6276 -2544 6270 -2535 6262 - 2517 6262 -2413 6263 -1728 6251 -603 6245 7 6246 L 8 17 16 1 2 421 0 0 -10023 -857-10023 -845-10021 -828-10020 -818-10017 -805- 10014 -793 -10016 -779-10021 -770-10028 -767-10032 -757-10026 -749- 10015 -741 -10001 -736 -9987 -729 -9979 -727 -9969 -722 -9958 -715 - 9954 -704 -9953 -689 -9960 -680 -9966 -659 -9972 -644 -9977 -631 - 9977 -616 -9975 -603 -9969 -587 -9966 -569 -9962 -553 -9961 -538 - 9965 -528 -9968 -515 -9972 -499 -9983 -465 -9983 -445 -9983 -436 - 9981 -428 -9976 -423 -9972 -418 -9969 -411 -9969 -402 -9970 -397 - 9973 -385 -9977 -378 -9980 -367 -9980 -360 -9979 -354 -9975 -344 - 9970 -333 -9966 -326 -9958 -312 -9949 -300 -9946 -291 -9946 -284 - 31 9947 -277 -9948 -270 -9948 -255 -9938 -244 -9936 -243 -9934 -238 - 9934 -231 -9938 -218 -9950 -209 -9961 -201 -9970 -194 -9974 -187 - 9978 -176 L 9 16 15 1 2 158 0 0 APPENDIX G.--Sample DLG data file (Standard Distribution Format)--continued -10031 3973-10032 3984-10034 4003-10037 4012-10038 4027- 10031 4035 -10023 4038-10016 4043-10011 4048-10004 4055 -9989 4062 - 9980 4063 -9974 4075 -9978 4084 -9992 4099-10003 4107-10019 4119- 10029 4134 -10033 4145-10037 4158-10044 4176-10046 4190-10049 4203- 10062 4212 -10077 4231-10078 4248-10079 4262-10079 4271-10082 4287- 10089 4305 -10093 4326-10095 4335-10098 4344-10097 4359-10094 4372- 10085 4387 -10076 4396-10068 4401-10059 4411-10054 4418-10051 4439- 10056 4449 -10058 4460-10073 4486-10073 4504-10074 4527-10068 4543- 10063 4554 -10053 4565-10039 4578-10018 4591 -9998 4603 -9958 4618 - 9925 4637 -9908 4649 -9894 4659 -9881 4661 -9876 4659 -9861 4652 - 9856 4646 -9850 4642 -9842 4639 -9824 4649 -9807 4657 -9792 4668 - 9768 4676 -9742 4677 -9720 4674 -9699 4659 -9666 4640 -9631 4615 - 9617 4604 -9597 4601 -9573 4608 -9563 4610 -9547 4612 -9532 4609 - 9518 4611 -9513 4613 -9504 4620 -9494 4628 -9488 4633 -9484 4637 - 9477 4642 -9460 4646 -9436 4644 -9419 4636 -9413 4631 -9404 4622 - 9398 4611 -9394 4600 -9390 4593 -9388 4585 -9384 4578 -9373 4574 - 9366 4571 -9358 4566 -9351 4560 -9344 4540 -9335 4532 -9331 4520 - 9326 4508 -9325 4491 -9327 4474 -9328 4463 -9328 4452 -9323 4441 - 9315 4433 -9294 4409 -9271 4386 -9250 4377 -9244 4372 -9237 4367 - 9228 4353 -9218 4345 -9207 4341 -9195 4337 -9179 4337 -9164 4337 - 9148 4342 -9136 4349 -9122 4352 -9110 4358 -9095 4358 -9082 4359 - 32 9057 4361 -9043 4367 -9033 4377 -9022 4393 -9012 4417 -9004 4447 - 9000 4465 -9000 4484 -8990 4513 -8982 4540 -8977 4551 -8970 4564 - 8961 4578 -8954 4591 -8942 4605 -8923 4627 -8911 4645 -8905 4658 - 8895 4674 -8886 4689 -8875 4700 -8869 4708 -8864 4714 -8857 4719 - 8848 4728 -8846 4738 -8845 4762 -8827 5100 -8788 5898 -8771 6255 - 8754 6485 -7383 6418 -5201 6334 L 10 14 10 1 2 17 0 0 7 6246 391 6245 1156 6251 1872 6258 2457 6264 2815 6269 3629 6289 3676 6290 3684 6289 3692 6286 3700 6283 3706 6278 3712 6273 3719 6270 3744 6271 3858 6276 4036 6283 L 11 10 12 1 2 26 0 0 4036 6283 4303 6291 4628 6299 5063 6316 5443 6328 6150 6349 6791 6375 7331 6399 7927 6426 8231 6439 8680 6468 9248 6502 9900 6547 10261 6570 10406 6581 10452 5824 10479 5460 10425 5459 10456 4873 10483 4594 10494 4465 10508 4183 10528 3917 10538 3716 10604 2704 10635 2183 L 12 11 17 1 2 333 0 0 1 -6187 -1739 -6193 -3872 -6160 -3919 -6144 -8111 -4445- 10703 -3356 -10696 -3344-10694 -3333-10691 -3324-10687 -3315-10681 -3305- 10674 -3295 -10667 -3285-10667 -3273-10674 -3267-10682 -3260-10686 -3250- 10684 -3242 APPENDIX G.--Sample DLG data file (Standard Distribution Format)--continued -10677 -3242-10669 -3240-10664 -3239-10656 -3235-10652 -3220- 10651 -3206 -10653 -3194-10656 -3185-10658 -3175-10659 -3169-10658 -3158- 10656 -3149 -10654 -3138-10655 -3128-10656 -3117-10658 -3108-10659 -3097- 10659 -3086 -10659 -3076-10657 -3066-10651 -3057-10644 -3053-10633 -3047- 10621 -3045 33 -10613 -3046-10604 -3039-10594 -3030-10587 -3020-10579 -3012- 10567 -2993 -10554 -2971-10547 -2961-10540 -2949-10532 -2938-10526 -2928- 10523 -2921 -10519 -2912-10515 -2904-10511 -2895-10504 -2885-10501 -2878- 10496 -2868 L 13 7 8 2 2 408 1 0 1307 -1163 1295 -1175 1286 -1188 1277 -1193 1265 -1194 1252 -1190 1238 -1187 1230 -1187 1223 -1192 1211 -1198 1199 -1203 1184 -1208 1176 -1213 1157 -1228 1136 -1243 1126 -1253 1117 -1261 1105 -1267 1092 -1275 1085 -1277 1073 -1274 1062 -1270 1052 -1270 1039 -1272 1022 -1279 1012 -1279 998 -1278 982 -1274 970 -1273 954 -1270 946 -1270 932 -1268 933 -1258 935 -1248 933 -1244 921 -1233 913 -1228 905 -1216 905 -1213 912 -1203 923 -1198 941 -1199 957 -1203 963 -1200 970 -1196 976 -1186 982 -1180 983 -1179 984 -1179 992 -1170 1006 -1162 1018 -1155 1042 -1145 1055 -1137 1057 -1118 1048 -1109 1040 -1100 1033 -1093 1026 -1090 1017 -1084 APPENDIX H.--Sample DLG data file (Optional Distribution Format) USGS-NMD DLG DATA - CHARACTER FORMAT - 09-29-82 VERSION ARIZONA AND NEW MEXICO 1967, 1972 2000000. 3 3 9999 2 0.50800000000D+02 4 0 4 1 0.637820640000000D+07 0.676865799729109D-02 0.290300000000000D+08 0.450300000000000D+08 -0.960000000000000D+08 0.230000000000000D+08 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.10000000000D+01 0.0 0.0 0.0 SW 31.000000 -115.000000 -1797041.23 1060722.79 NW 37.000000 -115.000000 -1663912.33 1717538.20 NE 37.000000 -103.000000 -616637.88 1573376.51 SE 31.000000 -103.000000 -665924.44 905019.85 HYPSOGRAPHY 0 18 18 010 2 2 010 13 13 1 N 1 -1797041.23 1060722.79 0 0 0 N 2 -1663912.33 1717538.20 0 0 0 N 3 -616637.88 1573376.51 0 0 0 34 N 4 -665924.44 905019.85 0 0 0 N 5 -1153236.44 1135937.23 2 0 0 1 2 N 6 -1205386.66 999226.66 3 0 0 -1 -5 6 N 7 -1128160.20 1246581.47 2 0 0 -2 13 N 8 -1129360.17 1377559.74 2 0 0 -3 -13 N 9 -977696.76 1517852.98 2 0 0 3 -4 N 10 -939239.49 1602400.23 3 0 0 4 -10 11 N 11 -1228689.21 1002793.31 2 0 0 -6 12 N 12 -635544.10 1350350.81 2 0 0 5 -11 N 13 -880370.63 1593835.17 0 0 0 N 14 -1142257.40 1628449.16 2 0 0 -7 10 N 15 -1403743.18 1668956.33 2 0 0 7 -9 N 16 -1663171.41 1583597.66 2 0 0 -8 9 N 17 -1696228.73 1340469.89 2 0 0 8 -12 N 18 -617232.22 1570176.46 -27 0 0 A 1 -1153183.85 1587442.82 8 0 1 0 0 -12 -6 -5 -11 -10 -7 -9 -8 0 0 APPENDIX H.--Sample DLG data file (Optional Distribution Format)--continued A 2 -1150562.93 1463806.99 8 0 0 0 0 12 8 9 7 10 11 5 6 L 1 5 6 2 2 334 1 0 -1153236.44 1135937.23 -1153966.87 1135473.71 -1154351.95 1134911.37 -1154737.04 1134349.03 -1155123.95 1134145.89 -1155568.12 1133899.36 -1156040.00 1133451.52 -1156423.25 1132529.98 -1156541.02 1131674.44 -1156559.97 1131164.26 -1156658.79 1130818.91 -1157009.23 1130508.19 -1157281.64 1130391.85 -1157567.91 1130174.86 -1157888.81 1129706.25 -1158095.21 1129324.42 -1158308.53 1128892.28 -1158443.82 1128654.50 -1158629.44 1128423.66 -1158881.06 1128458.30 -1159283.67 1128513.72 -1159821.56 1128331.36 -1160437.49 1127954.64 -1160716.83 35 1127787.97 -1160989.24 1127671.63 -1161204.40 1127598.69 -1161396.94 1127317.52 -1161546.08 1126979.10 -1161608.43 1126526.17 -1161700.32 1126231.14 -1161899.79 1125899.65 -1161998.61 1125554.30 -1161982.92 1125295.74 -1161679.13 1124894.97 -1161368.42 1124544.52 -1160962.15 1123770.69 290 2017 L 2 5 7 2 2 364 1 0 -1153236.44 1135937.23 -1152728.09 1136277.49 -1152355.02 1136379.97 -1151794.52 1136354.10 -1151542.89 1136319.46 -1151378.06 1136399.33 -1150991.14 1136602.46 -1150633.77 1136963.50 -1150326.72 1137331.47 -1150177.57 1137669.89 -1150007.65 1138159.29 -1149851.58 1138548.04 -1149716.29 1138785.81 -1149443.88 1138902.15 -1149070.82 1139004.64 -1148532.92 1139186.99 -1148217.12 1139246.07 -1147887.45 1139405.81 -1147601.19 1139622.80 -1147401.72 1139954.30 -1147375.84 1140514.81 -1147480.16 1141247.07 -1147433.50 1141958.56 -1147631.54 1142755.01 -1147938.99 1143874.19 -1147986.05 1144649.86 -1147887.24 1144995.21 -1147760.71 1145541.86 -1147641.11 1146038.19 -1147219.55 1146492.95 -1145050.03 1157783.39 -1145202.84 1158163.38 -1145369.50 1158442.72 -1145899.04 1159438.64 -1145980.74 1159962.68 -1146126.62 1160392.99 -1145911.46 1160465.93 -1145458.53 1160403.58 -1144969.13 1160233.66 -1144495.42 1160322.29 -1143568.78 1160348.57 -1143159.25 1160343.47 -1142900.69 1160359.16 -1142781.09 1160855.49 -1143020.70 1161349.98 -1142951.42 1161853.24 -1142838.75 1162299.24 -1142616.66 1162422.51 -1142243.60 1162524.99 -1141971.19 1162641.33 -1141726.49 1162556.37 290 2017 L 3 9 8 2 2 461 1 0 -977696.76 1517852.98 -978191.26 1517613.37 -978729.15 1517431.02 -979065.74 1517220.96 -979430.04 1516809.59 -979945.32 1516419.01 -980314.72 1515598.11 -980585.29 1515122.57 -980842.02 1514747.67 -981069.20 1514214.87 -981303.30 1513631.75 -981502.77 1513300.25 36 -981844.46 1512680.66 -982120.13 1511795.58 -982631.74 1510686.59 -982966.50 1510117.32 -983287.40 1509648.70 -983622.16 1509079.43 -984482.79 1508787.67 -985825.89 1508716.16 -986716.06 1508582.30 -987885.57 1508281.77 -988444.25 1507948.44 -989211.15 1507592.50 -989632.71 1507137.74 -990010.86 1506625.72 -990762.08 1506011.22 APPENDIX H.--Sample DLG data file (Optional Distribution Format)--continued -991055.27 1505743.90 -991598.26 1505152.02 -992198.50 1504516.74 -993152.85 1504289.15 -993626.56 1504200.52 -994365.76 1504045.88 -995033.85 1504035.29 -996090.68 1504180.77 -996975.76 1504456.44 -997860.84 1504732.11 -998954.14 1504985.17 -999427.86 1504896.54 -1000281.56 1504655.10 -1001071.08 1504507.39 -1001983.87 1504581.76 -1002882.80 1504756.78 -1003983.03 1504959.51 -1004831.64 1505127.60 290 2017 L 4 10 9 2 2 229 1 0 -939239.49 1602400.23 -939662.88 1602304.67 -939992.54 1602144.93 -940530.44 1601962.58 -940896.57 1601910.42 -941392.90 1602030.02 -941795.50 1602085.44 -942371.70 1602369.87 -942637.18 1602303.86 -942923.45 1602086.87 -943237.42 1601668.58 -943278.99 1601366.63 -943247.61 1600849.51 -943200.55 1600073.85 -943422.63 1599950.58 -943745.37 1599841.17 -944182.61 1599644.96 -943901.44 1599452.42 -943490.07 1599088.12 -943179.36 1598737.68 -942731.52 1598265.80 -942665.51 1598000.31 -942670.61 1597590.78 -942524.72 1597160.47 -942406.55 1596528.85 -942290.21 1596256.44 -942187.73 1595883.38 -941861.33 1595274.38 -941894.13 1594663.54 -941940.79 1593952.06 -941925.10 1593693.50 -941829.55 1593270.12 -941834.64 1592860.58 290 2017 L 5 12 6 1 2 125 0 0 -635544.10 1350350.81 -636541.07 1334540.24 -637028.45 37 1327274.41 -637514.00 1319649.38 -637823.09 1314051.22 -638446.57 1309521.92 -639226.52 1306091.03 -639606.73 1300348.82 -640041.95 1292716.86 -640740.82 1284659.68 -640903.01 1281246.30 -641318.26 1276739.62 -641941.95 1266620.92 -642746.17 1256680.92 -643918.56 1241458.56 -645769.45 1219817.15 -646599.94 1210803.78 -647757.87 1199784.32 -648399.48 1191770.54 -649205.53 1182189.74 -650310.27 1173419.24 -650645.65 1168747.73 -651036.44 1163673.61 -652314.99 1149542.72 -653152.01 1138991.88 -654034.26 1128857.50 -654629.22 1121555.20 -655239.05 1111537.16 -655882.10 1102395.43 -656881.71 1089918.36 -657843.02 1076974.51 -658552.08 1068098.27 -659496.28 1056023.80 -660402.16 1043482.55 -661200.88 1032464.93 -662221.27 1019836.88 -662548.30 1016343.64 -693215.09 1018565.16 -726846.00 1021604.95 -736858.95 1022624.32 -745627.62 1023369.85 -752181.96 1023810.57 -756810.08 1024088.69 -760863.83 1024441.59 -769545.70 1025072.62 -776358.60 1025497.65 -786408.02 1026624.60 -792984.98 1027273.55 -802588.39 1028287.82 -813873.34 1029379.73 -818862.49 1030015.23 L 6 6 11 1 2 3 0 0 -1205386.66 999226.66 -1219923.81 1001279.04 -1228689.21 1002793.31 L 7 15 14 1 2 16 0 0 -1403743.18 1668956.33 -1384818.95 1665992.38 -1353217.77 1660873.16 -1315463.03 1655009.43 -1285796.84 1650361.68 -1273631.91 1648584.57 -1272545.53 1648281.19 -1272106.46 1648118.19 -1271235.23 1647741.87 APPENDIX H.--Sample DLG data file (Optional Distribution Format)--continued -1270471.59 1647329.08 -1270074.08 1646864.12 -1269168.22 1646739.43 -1263927.44 1646069.29 -1229537.57 1640720.03 -1172962.91 1632624.62 -1142257.40 1628449.16 L 8 17 16 1 2 421 0 0 38 -1696228.73 1340469.89 -1696145.60 1341073.79 -1695927.18 1341915.47 -1695807.58 1342411.80 -1695566.54 1343045.25 -1695332.43 1343628.37 -1695336.10 1344346.79 -1695525.38 1344834.35 -1695856.88 1345033.82 -1695988.90 1345564.79 -1695631.53 1345925.83 -1695022.53 1346252.23 -1694283.33 1346406.87 -1693530.28 1346662.17 -1693113.82 1346707.40 -1692575.93 1346889.75 -1691973.86 1347165.82 -1691696.35 1347691.70 -1691542.11 1348439.65 -1691832.05 1348941.07 -1691988.52 1350039.47 -1692186.56 1350835.92 -1692348.13 1351524.79 -1692244.22 1352279.68 L 9 16 15 1 2 158 0 0 -1663171.41 1583597.66 -1663145.53 1584158.16 -1663114.56 1585128.20 -1663203.19 1585601.92 -1663149.60 1586363.73 -1662741.90 1586717.84 -1662318.52 1586813.40 -1661931.60 1587016.53 -1661645.33 1587233.52 -1661244.56 1587537.31 -1660441.19 1587785.67 -1659981.33 1587773.65 -1659596.25 1588335.99 -1659735.20 1588816.63 -1660335.84 1589668.50 -1660834.01 1590147.31 -1661556.08 1590862.05 -1661955.43 1591686.21 -1662080.53 1592267.50 -1662191.77 1592949.45 -1662419.35 1593903.80 -1662423.02 1594622.21 -1662483.94 1595297.23 -1663075.82 1595840.21 -1663699.08 1596900.31 -1663631.64 1597762.77 -1663584.98 1598474.26 -1663522.63 1598927.19 -1663562.77 1599753.18 -1663790.35 1600707.53 -1663846.18 1601792.08 -1663884.48 1602258.86 -1663973.11 1602732.57 L 10 14 10 1 2 17 0 0 -1142257.40 1628449.16 -1122939.32 1625738.67 -1084398.72 1620741.07 -1048317.14 1616133.24 -1018835.14 1612382.59 -1000783.96 1610154.17 -959680.42 1605521.68 -957308.19 1605246.41 -956912.52 1605140.67 -956530.69 1604934.27 -956148.87 1604727.87 -955881.56 1604434.68 -955614.24 1604141.49 -955282.75 1603942.02 -954017.68 1603819.15 -948245.93 1603281.05 -939239.49 1602400.23 L 11 10 12 1 2 26 0 0 -939239.49 1602400.23 -925747.15 1600953.18 -909335.93 1599104.34 -887326.56 1596946.41 -868119.72 1594917.85 -832394.09 39 1591076.93 -799955.30 1587944.86 -772613.25 1585411.81 -742432.19 1582641.80 -727043.17 1581190.06 -704246.10 1579539.05 -675425.66 1577315.28 -642301.67 1575063.19 -623974.82 1573719.84 -616601.41 1573268.93 -619530.57 1534853.84 -620693.40 1516348.30 -623417.91 1516672.06 -625917.34 1486966.54 -626491.33 1472738.67 -626831.40 1466170.47 -628080.40 1451881.69 -628916.61 1438356.54 -629805.79 1428171.83 -633494.95 1376785.17 -635544.10 1350350.81 L 12 11 17 1 2 333 0 0 -1228689.21 1002793.31 -1316297.21 1014545.24 -1423412.98 1030982.38 -1425667.44 1032113.18 -1624862.24 1146656.44 -1747761.96 1219417.08 -1747326.56 1219972.49 -1747149.70 1220512.22 -1746936.38 1220944.37 APPENDIX H.--Sample DLG data file (Optional Distribution Format)--continued -1746672.73 1221369.59 -1746301.50 1221831.28 -1745879.94 1222286.04 -1745458.39 1222740.80 -1745375.26 1223344.71 -1745685.97 1223695.16 -1746040.09 1224102.85 -1746172.11 1224633.82 -1746016.04 1225022.57 -1745663.76 1224974.08 -1745247.30 1225019.31 -1744988.75 1225035.00 -1744558.43 1225180.88 -1744253.22 1225908.05 -1744105.91 1226605.68 -1744123.43 1227223.44 -1744212.06 1227697.15 -1744243.43 1228214.26 -1744252.19 1228523.15 -1744125.67 1229069.80 -1743962.67 1229508.87 -1743785.81 1230048.60 -1743766.86 1230558.78 -1743740.99 1231119.29 -1743779.29 1231586.08 -1743753.41 1232146.58 -1743677.21 1232700.17 L 13 7 8 2 2 408 1 0 -1128160.20 1246581.47 -1128847.24 1246060.69 -1129390.22 1245468.81 -1129877.79 1245279.53 -1130488.63 1245312.33 -1131115.15 1245603.69 -1131798.92 1245851.66 -1132201.53 1245907.08 -1132588.44 1245703.94 -1133233.91 1245485.12 -1133872.46 1245316.62 -1134661.98 1245168.91 -1135099.22 1244972.70 -1136159.32 1244349.44 -1137320.07 40 1243740.03 -1137892.60 1243306.05 -1138400.95 1242965.80 -1139046.42 1242746.97 -1139756.07 1242434.43 -1140122.21 1242382.27 -1140705.33 1242616.38 -1141231.20 1242893.88 -1141734.46 1242963.16 -1142402.54 1242952.56 -1143306.57 1242718.05 -1143809.83 1242787.33 -1144507.46 1242934.64 -1145284.95 1243246.78 -1145881.93 1243380.24 -1146666.36 1243642.05 -1147068.96 1243697.47 -1147759.67 1243895.11 -1147640.07 1244391.44 -1147470.14 1244880.84 -1147543.08 1245095.99 -1148070.78 1245732.71 -1148438.75 1246039.75 -1148758.22 1246699.08 -1148737.44 1246850.06 290 2017 APPENDIX I.--Data Sources and Currency The published 1:2,000,000-scale National Atlas sectional maps were completely revised in l972-73. Selected information from these maps was revised before digitizing. The source and date of the updated information are presented below: Category Source Currency of Data Political Boundaries, Alaskan borough boundaries Bureau of the Census 1979 Administrative Boundaries Administering Federal Various agency Roads and Trails Various 1980 Railroads Interstate Commerce 1979 Commission Streams,Alaska Landsat imagery 1979 Water Bodies, major reservoirs National Oceanic and 1979-80 Atmospheric Administration Sectional Aeronautical Charts Cultural Features, airports Federal Aviation Administration 1980 Alaska pipeline USGS maps 1979 41