Web Map Service

Web Map Service
Name	Web Map Service
Developer	Open Geospatial Consortium
Released	19 April 2000
Latest release version	1.3.0
Latest release date	15 March 2004
Genre	Geographic information system

Web Map Service. A Web Map Service is a standard protocol developed by the Open Geospatial Consortium for serving georeferenced map images over the Internet. It enables a client-server architecture where a client, such as a web browser or GIS software, can request customized maps from one or more remote servers. The service generates images, typically in formats like Portable Network Graphics or Graphics Interchange Format, that are dynamically rendered from underlying geospatial data.

Overview

The protocol was formally adopted as an international standard by the International Organization for Standardization under ISO 19128. Its primary function is to provide a standardized method for clients to request maps, which are returned as static images rather than raw vector data. This model is fundamental to many online mapping platforms and supports the creation of composite maps by overlaying layers from multiple, distributed servers. The development of this specification was heavily influenced by earlier efforts in distributed computing and interoperability within the geospatial community.

Technical specifications

The core of the specification is defined by a set of mandatory and optional operations communicated via HTTP. Requests are made using key-value pairs in a Uniform Resource Locator, adhering to a defined application programming interface. The protocol specifies parameters for defining the geographic bounding box, output image size, coordinate reference system using Spatial Reference System Identifier codes, and requested layers. Critical elements of the server's capabilities are described in an XML-based metadata document, which details available layers, styles, and supported Coordinate Reference Systems.

Operations

The standard mandates two essential operations for basic compliance. The first operation retrieves the service metadata, which describes the server's content and acceptable request parameters. The second operation is the primary mechanism for requesting a map image, where the client specifies the layers, spatial extent, output size, and format. An optional third operation provides information about features displayed at a specific pixel location, though this is not required for basic map rendering. These operations enable complex, multi-source mapping applications within frameworks like NASA WorldWind or commercial GIS software.

Data formats

Servers typically return rendered map images in raster formats. Common formats include Portable Network Graphics for lossless compression, Graphics Interchange Format for simple images, and JPEG for photographic or complex imagery. Some implementations may also support Scalable Vector Graphics for vector-based output. The specification does not dictate the internal data formats used by the server; these can range from Shapefile and GeoPackage to enterprise databases like PostgreSQL with the PostGIS extension or Oracle Spatial.

Implementations and usage

Numerous open-source and proprietary software packages implement the protocol. Prominent open-source servers include GeoServer, MapServer, and QGIS Server, while commercial solutions are offered by Esri in its ArcGIS suite and Hexagon AB through ERDAS IMAGINE. Clients that consume these services range from lightweight JavaScript libraries like OpenLayers and Leaflet to full-featured desktop applications such as QGIS and ArcGIS Pro. The service is widely used by national mapping agencies like the United States Geological Survey and the Ordnance Survey, as well as in scientific projects such as those led by NASA.

Standards and interoperability

This protocol is a foundational member of the Open Geospatial Consortium's suite of interoperability standards, which includes the Web Feature Service for vector data and the Web Coverage Service for raster data. Its profiles and extensions ensure compatibility with other frameworks, such as the OpenGIS specifications for Catalog Service for the Web. Conformance with this standard ensures that diverse systems, from European Space Agency platforms to local government Spatial Data Infrastructure, can exchange and visualize map data seamlessly, promoting the ideals of the Global Earth Observation System of Systems.

Category:Geographic information systems Category:Web services Category:Open Geospatial Consortium standards Category:ISO standards