Project DescriptionThe Open Geospatial Consortium/Web Map Service is a specification developed
by the Open Geospatial Consortium that defines three WMS operations:
1. GetCapabilities returns service-level metadata, which is a
description of the service's information content and acceptable
2. GetMap returns a map image whose geospatial and dimensional
parameters are well defined;
3. GetFeatureInfo (optional) returns information about
particular features shown on a map.
This specification defines a syntax for World Wide Web (WWW) Uniform Resource
Locators (URLs) that invoke each of these operations. Also, an Extensible
Markup Language (XML) encoding is defined for service-level metadata.
When requesting a map, a client may specify the information to be shown on the
map (one or more "Layers"), possibly the "Styles" of those Layers, what portion
of the Earth is to be mapped (a "Bounding Box"), the projected or geographic
coordinate reference system to be used (the "Spatial Reference System," or
SRS), the desired output format, the output size (Width and Height), and
background transparency and color. When two or more maps are produced with the
same Bounding Box, Spatial Reference System, and output size, the results can
be accurately layered to produce a composite map. The use of image formats that
support transparent backgrounds allows the lower Layers to be visible.
Furthermore, individual map Layers can be requested from different Servers. The
WMS specification thus enables the creation of a network of distributed Map
Servers from which Clients can build customized maps.
A particular WMS provider in a distributed WMS network need only be the steward
of its own data collection. This stands in contrast to vertically integrated
web mapping sites that gather in one place all of the data to be made
accessible by their own private interface.