OGC WMS

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This is a draft how a standards intro page could look like

Contents

What Can You Do With It?

The OGC Web Map Server (WMS) standard defines how to request map images over HTTP. The maps are generated dynamically on the server with each request and can therefore be heavily parameterized. This sets the WMS standard apart from static map servers delivering pre-rendered map images in small tiles which are stitched into one image by the client.

Primary Use Cases

The standard makes map images available and accessible through a highly configurable interface in standard image formats. Government agencies publish all kinds of official map cartography using this standard. Other large organizations use this standard to enable independent departments to interact more easily internally. Anybody using this standard can use it to overlay map data from many different sources regardless of the underlying software.

Maturity of the standard

The WMS standard has been implemented by most map serving software packages, see the product statistics. There is an abundance of client software packages. Many web sites, portal and apps have WMS interface. The standard is an integral component of several major government policies (e.g. GD-DE in Germany, INSPIRE in Europe, etc.).

Primary API Calls

There are two main API calls:

  • GetCapabilities: It returns an XML document containing all information to make an educated call to the GetMap request.
  • GetMap: It returns a dynamically rendered map image according to the parameters (and the server capacities).

GetMap Example

The example map below shows a map of southern Great Britain. It is rendered dynamically every time the browser requests the image (ignoring caches and proxies). Any data changes on the server side become visible immediately when the page is reloaded, be it temperature, weather warning, traffic information, GPD position of a vehicle or any other data that was updated on the server in the meantime.

Note
Error messages can be returned as text or printed into an image with the requested map size. This is helpful if the WMS client cannot display the text message.

Optional Requests

  • GetFeatureInfo: Queries the server for features in a specified layer for a specified location. The location is a pixel coordinate in the map image which is transformed into coordinates by the server.
  • GetLegend: Request a legend image for a specified layer.
  • Get ...

Links

Related standards

  • Web Map Tile Server (WMTS): For highly scalable systems which only need static maps the WMTS standard is a better fit. It complements the WMS standard with cachable static map tiles. WMS server can be used as data sources / rendering engines for WMTS.
  • Web Feature Service (WFS): For extended query functionality of map content the WFS standard is a better fit. It complements the WMS by giving access to geographic features of the same map. WMS and WFS often go together. Having two separate endpoints allows to easily separate map and feature access to different user groups.
  • Styled Layer Descriptor: This standard allows the user to modify the cartographic appearance of a map image. It is an optional feature of the OGC WMS standard.
  • Symbology Encoding: This standard describes hwo to define map symbology and is used modify the cartographic appearance of map images. It is an optional feature of the OGC WMS and SLD standards.
  • etc...