What is a WMS?

A Web Map Service (WMS) provides versatile access to geographic datasets using standards from the Open GIS Consortium.

Produce Maps

A WMS displays 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.  This contrasts to a Web Feature Service (WFS), which returns the actual data.

Why Use a WMS?

Using a WMS service means you don't need to download and store very large files on your own computer.

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 allows underlying maps to be visible.  Individual maps can be requested from different servers.  The Web Map Service thus becomes a powerful visualization tool that enables the creation of a network of distributed map servers from which clients can build customized maps.

How to Use a WMS

WMS operations can be invoked using a standard web browser by submitting requests in the form of a Uniform Resource Locator (URL).  A Web Map Service, however, is usually not invoked directly.  More often, it is requested by a client application that provides the user with interactive controls.  ArcIMS and Minnesota MapServer are examples of web-based WMS clients.  But a client application does not have to be web-based.  ESRI’s ArcGIS, AutoDesk’s AutoCAD and MapINFO are all popular geospatial data processing software products that contain WMS connector clients.


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