Map Viewer Technical Details

The Map Viewer is implemented as as a perl script that accepts requests for map renderings and returns an HTML document including an inlined GIF image of the requested map. It is running as part of a custom inetd-invoked HTTP daemon running on the host mapweb.parc.xerox.com at the Xerox Palo Alto Research Center in California.

The map images are generated on the fly by the mapwriter program which is a stand-alone Unix command which produces raster map images from either of two publically available vector map databases. Options controlling the map renderings are encoded into the W3 URL strings and passed as command line arguments to the mapwriter program. Efficient conversion to GIF format is provided by a program called rastogif contributed by James Woods (jaws@dme.nt.gov.au). A small static cache is used for a few of the most frequently requested map images.

For a list of the colors used for various map features, see World Map Legend and U.S.A. Map Legend.

URL Format

http://hostname/map/option=value/.../option=value

Rendering Options

/db=database_name

the database name, either world or usa

/lat=latitude_center

the center latitude for the map in degrees (negative for south, default 0)

/lon=longitude_center

the center longitude for the map in degrees (negative for west, default 0)

/ht=latitude_extent

the height of the map in degrees (default 180)

/wd=longitude_extent

the width of the map in degrees (default 360)

/iwd=image_width

the width of the map image in pixels (default 512)

/iht=image_height

the height of the map image in pixels (default 256)

/color

generate color raster images

/bw

generate monochrome bitmaps (default)

/noview

do not show the map as an inlined image (speeds up changing options)

/view

show the map as an inlined image (default)

/nozoom

do not zoom in on position selections

/autozoom=zoom_factor

change the zoom factor for position selections

/all

show all map featues

/def

show default map featues

/feature_name

show the named feature (e.g. coast, border, river, road, RR, fed.)

/feature_name=0

do not show the named feature

/nogrid

do not show the map graticule (lines of latitude/longetude)

/grid

show the graticule unless zoomed very far in (default)

/mark=latitude,longitude,mark_type,mark_size

place a mark on the map. ",mark_type" (1..7) and ",mark_size" (in pixels) are optional. multiple marks can be separated by ";" (see example below).

?xpos,ypos

specifies a position selection within a map image in pixel coordinates (generated from ISMAP inlined images). This must occur last in the URL.

/format=.gif

used when requesting just an image, rather than an HTML document. This must occur last in the URL.

URL Examples

/map

Produces the default world map image in a hypertext document.

/map/format=.gif

Produces just the GIF image (displayed in a separate viewer in Mosaic).

/map/db=usa/color/ht=1/wd=2/lat=37.8/lon=-122

A map of the San Francisco Bay Area.

/map/db=usa/color/ht=1/wd=2/lat=37.8/lon=-122?ht=.5+wd=1

The same map with the map scale overridden from the search query field.

/map/lat=-40.60/lon=-172.35/ht=15/wd=12/iht=150/iwd=128

A small map of New Zealand.

/map/color/mark=37.40,-122.14;21.35,-157.97

Specifies marks for Palo Alto, California and Pearl Harbor, Hawaii.

Bugs

• A scrambled image results for values of iwd that are not a multiple of 8 (e.g. iwd=100). The server has been patched to round up widths.
• The "Requested region" reported will be smaller than the displayed region if the image aspect ratio does not match the latitude/longitude extent (in degrees).
• Meridian lines are displayed relative to the center longitude of the current map, rather than at standard multiples of degrees.

Enhancements

• This interface does not take advantage of the HTML/HTTP extensions for fill-in-the-blank forms.