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Proactive disclosure Print version   | |  Geoscience Data Repository About WMS Services
The Open Geospatial Consortium (OGC) defines WMS as follows:
A Web Map Service (WMS) produces maps of spatially referenced data dynamically
from geographic information. This International Standard defines a "map"
to be a portrayal of geographic information as a digital image file suitable
for display on a computer screen. A map is not the data itself. WMS-produced
maps are generally rendered in a pictorial format such as PNG, GIF or
JPEG, or occasionally as vector-based graphical elements in Scalable Vector
Graphics (SVG) or Web Computer Graphics Metafile (WebCGM) formats.
This international standard defines three operations:
Web Map Service operations can be invoked using a standard web browser by submitting requests in the form of Uniform Resource Locators (URLs). The content of such URLs depends on which operation is requested. In particular, when requesting a map the URL indicates what information is to be shown on the map, what portion of the Earth is to be mapped, the desired coordinate reference system, and the output image width and height. When two or more maps are produced with the same geographic parameters and output size, the results can be accurately overlaid to produce a composite map. The use of image formats that support transparent backgrounds (e.g., GIF or PNG) allows underlying maps to be visible. Furthermore, individual maps can be requested from different servers. The Web Map Service thus enables the creation of a network of distributed map servers from which clients can build customized maps. This International Standard applies to a Web Map Service that publishes its ability to produce maps rather than its ability to access specific data holdings. A basic WMS classifies its geographic information holdings into "Layers" and offers a finite number of predefined "Styles" in which to display those layers. This International Standard supports only named Layers and Styles, and does not include a mechanism for user-defined symbolization of feature data. Note: The Open GIS Consortium (OGC) Styled Layer Descriptor (SLD) specification defines a mechanism for user-defined symbolization of feature data instead of named Layers and Styles. In brief, an SLD-enabled WMS retrieves feature data from a Web Feature Service and applies explicit styling information provided by the user in order to render a map. See also: Alternate access to GDR data
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