What’s a web map service?

The OpenGIS® specification for a web map service defines three operations:

1. GetCapabilities returns metadata that describes the data that is available and defines the acceptable request parameters.
   
   
2. GetMap returns a map image of the requested layers. Some parameters include size, projection, geographic area and image format.
   
   
3. GetFeatureInfo (optional) returns detailed attribute information about features shown on a map.

The specification defines syntax for World Wide Web (WWW) Uniform Resource Locators (URLs) that invoke each of these operations. It also defines an XML encoding for service-level metadata.

When two or more maps are produced with the same bounding box, spatial reference system and output size, the results can be layered to produce a composite map. Individual map layers can be requested from different servers. In this way, clients can build customized maps from a network of distributed map servers.

Click to read the OpenGIS® Web Map Service Implementation Specification.

An overview of this specification is available on the GeoConnections web site.

Did you know? As discussed in Module 3, Standards-based Web Development, the Open Geospatial Consortium, Inc. (OGC) is an international consortium of over 250 companies, government agencies and universities participating in a consensus process to develop publicly available interface specifications. Through OGC, expert GIS and web mapping technology users work with geospatial software vendors, earth imaging vendors, database software vendors, integrators, computer vendors and other technology providers to reach agreement on the technical details of open web mapping interfaces that allow these systems to work together over the Web. The Canadian Geospatial Data Infrastructure is a participant in OGC. It monitors developments closely and strives to adopt standards as quickly as possible to ensure that the needs of Canadian geospatial users are being met.