Returns an image in formats such as png, jiff, etc
The WMS service interprets the GML file and present the "feature"
on the map
A feature can be something like a road, a lake or building
GetMap (required) -- returns a picture
The GetMap request returns a map image whose geospatial and dimensional parameters are well defined. The map operation of the GetMap request is
invoked by a client to get a rectangular set of pixels. These pixels contain a picture of a map covering a geographic area or a set of graphic
elements that lie in a geographic area. The GetMap request allows the WMS client to specify distinct layers, the spatial reference system (SRS), the
geographic area, and other parameters describing the returned map format. Upon receiving the GetMap request, a WMS server will either satisfy the
request or throw an exception in accordance with the exception instructions contained in the GetMap request.
GetCapabilities (required) -- what's avaiable
The GetCapabilities request returns the WMS server's service-level metadata, which is a machine-readable (and human-readable), description of the WMS
service's information content and acceptable request parameters. The response to a GetCapabilities request is general information about the service itself
and specific information about the available maps. This response is the "capabilities" document, which is an XML configuration file that is provided
to requesting WMS clients. This XML file is the metadata about a WMS server indicating its data holdings and abilities.
GetFeature (optional) -- returns attribute information
The GetFeatureInfo request returns information about particular features shown on a map. If a WMS server supports this operation, its maps are said
to be "queryable," and a WMS client can request information about features on a map by adding to the map URL additional parameters specifying a location
(as an X, Y offset from the upper left corner) and the number of nearby features about which to return information.