About WMS - Web Map Server

All about GIS Web Map Server (WMS)

WMS stands for Web Map Server. It's a standard protocol for serving Geo referenced map images online. We can generate wms by a map server using data from a GIS database or from a .tab file. There are following popular open source software that provide web map services capability.

• MapServer

• GeoServer

• Geozilla

• Quantum GIS Server

A WMS server usually serves the map in a bitmap format, e.g. PNG, GIF or JPEG. In addition, vector graphics can be included: such as points, lines, curves and text, expressed in SVG or WebCGM format.

WMS specifies the following number of different request types

• GetCapabilities - It returns parameters about the WMS (such as map image format and WMS version compatibility) and the available layers (map bounding box, coordinate reference systems, URI of the data and whether the layer is mostly opaque or not)

• GetMap - It returns a map image. and parameters include: width & height of the map, coordinate reference system, rendering style, image format.

Some of the following request may optionally supports:

• GetFeatureInfo - If a layer is marked as 'Queryable'(mouse click) then you can request data about a coordinate of the map image.

• GetLegendGraphic - It return an image of the map's legend image, giving a visual guide to map elements.

• DescribeLayer

Fore more information visit http://mapserver.org/ogc/wms_server.html

Notes:

1. A WMS layer is a raster layer!
2. Data is not required.
3. Query template files (Header, Template, and Footer) are not allowed because the layer is raster.
4. PROJECTION has to be specified even if it is the same than the global CRS.
5. Don't define STYLE and LABEL objects, because they are already set within the WMS Server.
6. wms_name corresponds to the NAME parameter of the Layer Object within the WMS server map file.