WMS reference

Introduction

The OGC Web Map Service (WMS) specification defines an HTTP interface for requesting georeferenced map images from a server. GeoServer supports WMS 1.1.1, the most widely used version of WMS, as well as WMS 1.3.0.

The relevant OGC WMS specifications are:

GeoServer also supports some extensions to the WMS specification made by the Styled Layer Descriptor (SLD) standard to control the styling of the map output. These are defined in:

Benefits of WMS

WMS provides a standard interface for requesting a geospatial map image. The benefit of this is that WMS clients can request images from multiple WMS servers, and then combine them into a single view for the user. The standard guarantees that these images can all be overlaid on one another as they actually would be in reality. Numerous servers and clients support WMS.

Operations

WMS requests can perform the following operations:

Operation Description
Exceptions If an exception occur
GetCapabilities Retrieves metadata about the service, including supported operations and parameters, and a list of the available layers
GetMap Retrieves a map image for a specified area and content
GetFeatureInfo (optional) Retrieves the underlying data, including geometry and attribute values, for a pixel location on a map
DescribeLayer (optional) Indicates the WFS or WCS to retrieve additional information about the layer.
GetLegendGraphic (optional) Retrieves a generated legend for a map

Exceptions

Formats in which WMS can report exceptions. The supported values for exceptions are:

Format Syntax Notes
XML EXCEPTIONS=application/vnd.ogc.se_xml Xml output. (The default format)
INIMAGE EXCEPTIONS=application/vnd.ogc.se_inimage Generates an image
BLANK EXCEPTIONS=application/vnd.ogc.se_blank Generates a blank image
PARTIALMAP EXCEPTIONS=application/vnd.gs.wms_partial This is a GeoServer vendor parameter and only applicable for getMap requests. Returns everything that was rendered at the time the rendering process threw an exception. Can be used with the WMS Configuration Limits to return a partial image even if the request is terminated for exceeding one of these limits. It also works with the timeout vendor parameter.
JSON EXCEPTIONS=application/json Simple Json representation.
JSONP EXCEPTIONS=text/javascript Return a JsonP in the form: paddingOutput(...jsonp...). See WMS vendor parameters to change the callback name. Note that this format is disabled by default (See Global variables affecting WMS).

GetCapabilities

The GetCapabilities operation requests metadata about the operations, services, and data (“capabilities”) that are offered by a WMS server.

The parameters for the GetCapabilities operation are:

Parameter Required? Description
service Yes Service name. Value is WMS.
version Yes Service version. Value is one of 1.0.0, 1.1.0, 1.1.1, 1.3.
request Yes Operation name. Value is GetCapabilities.

GeoServer provides the following vendor-specific parameters for the GetCapabilities operation. They are fully documented in the WMS vendor parameters section.

Parameter Required? Description
namespace No limits response to layers in a given namespace

A example GetCapabilities request is:

http://localhost:8080/geoserver/wms?
service=wms&
version=1.1.1&
request=GetCapabilities

There are three parameters being passed to the WMS server, service=wms, version=1.1.1, and request=GetCapabilities. The service parameter tells the WMS server that a WMS request is forthcoming. The version parameter refers to which version of WMS is being requested. The request parameter specifies the GetCapabilities operation. The WMS standard requires that requests always includes these three parameters. GeoServer relaxes these requirements (by setting the default version if omitted), but for standard-compliance they should always be specified.

The response is a Capabilities XML document that is a detailed description of the WMS service. It contains three main sections:

Service Contains service metadata such as the service name, keywords, and contact information for the organization operating the server.
Request Describes the operations the WMS service provides and the parameters and output formats for each operation. If desired GeoServer can be configured to disable support for certain WMS operations.
Layer Lists the available coordinate systems and layers. In GeoServer layers are named in the form “namespace:layer”. Each layer provides service metadata such as title, abstract and keywords.

GetMap

The GetMap operation requests that the server generate a map. The core parameters specify one or more layers and styles to appear on the map, a bounding box for the map extent, a target spatial reference system, and a width, height, and format for the output. The information needed to specify values for parameters such as layers, styles and srs can be obtained from the Capabilities document.

The response is a map image, or other map output artifact, depending on the format requested. GeoServer provides a wide variety of output formats, described in WMS output formats.

The standard parameters for the GetMap operation are:

Parameter Required? Description
service Yes Service name. Value is WMS.
version Yes Service version. Value is one of 1.0.0, 1.1.0, 1.1.1, 1.3.
request Yes Operation name. Value is GetMap.
layers Yes Layers to display on map. Value is a comma-separated list of layer names.
styles Yes Styles in which layers are to be rendered. Value is a comma-separated list of style names, or empty if default styling is required. Style names may be empty in the list, to use default layer styling.
srs or crs Yes Spatial Reference System for map output. Value is in form EPSG:nnn. crs is the parameter key used in WMS 1.3.0.
bbox Yes Bounding box for map extent. Value is minx,miny,maxx,maxy in units of the SRS.
width Yes Width of map output, in pixels.
height Yes Height of map output, in pixels.
format Yes Format for the map output. See WMS output formats for supported values.
transparent No Whether the map background should be transparent. Values are true or false. Default is false
bgcolor No Background color for the map image. Value is in the form RRGGBB. Default is FFFFFF (white).
exceptions No Format in which to report exceptions. Default value is application/vnd.ogc.se_xml.
time No Time value or range for map data. See Time Support in GeoServer WMS for more information.
sld No A URL referencing a StyledLayerDescriptor XML file which controls or enhances map layers and styling
sld_body No A URL-encoded StyledLayerDescriptor XML document which controls or enhances map layers and styling

GeoServer provides a number of useful vendor-specific parameters for the GetMap operation. These are documented in the WMS vendor parameters section.

Example WMS request for topp:states layer to be output as a PNG map image in SRS EPGS:4326 and using default styling is:

http://localhost:8080/geoserver/wms?
request=GetMap
&service=WMS
&version=1.1.1
&layers=topp%3Astates
&styles=population
&srs=EPSG%3A4326
&bbox=-145.15104058007,21.731919794922,-57.154894212888,58.961058642578&
&width=780
&height=330
&format=image%2Fpng

The standard specifies many of the parameters as being mandatory, GeoServer provides the WMS Reflector to allow many of them to be optionally specified.

Experimenting with this feature is a good way to get to know the GetMap parameters.

Example WMS request using a GetMap XML document is:

<?xml version="1.0" encoding="UTF-8"?>
<ogc:GetMap xmlns:ogc="http://www.opengis.net/ows"
            xmlns:gml="http://www.opengis.net/gml"
   version="1.1.1" service="WMS">
   <StyledLayerDescriptor version="1.0.0">
      <NamedLayer>
        <Name>topp:states</Name>
        <NamedStyle><Name>population</Name></NamedStyle>
      </NamedLayer>
   </StyledLayerDescriptor>
   <BoundingBox srsName="http://www.opengis.net/gml/srs/epsg.xml#4326">
      <gml:coord><gml:X>-130</gml:X><gml:Y>24</gml:Y></gml:coord>
      <gml:coord><gml:X>-55</gml:X><gml:Y>50</gml:Y></gml:coord>
   </BoundingBox>
   <Output>
      <Format>image/png</Format>
      <Size><Width>550</Width><Height>250</Height></Size>
   </Output>
</ogc:GetMap>

Time

As of GeoServer 2.2.0, GeoServer supports a TIME attribute for WMS GetMap requests as described in version 1.3 of the WMS specification. This parameter allows filtering a dataset by temporal slices as well as spatial tiles for rendering. See Time Support in GeoServer WMS for information on its use.

GetFeatureInfo

The GetFeatureInfo operation requests the spatial and attribute data for the features at a given location on a map. It is similar to the WFS GetFeature operation, but less flexible in both input and output. Since GeoServer provides a WFS service we recommend using it instead of GetFeatureInfo whenever possible.

The one advantage of GetFeatureInfo is that the request uses an (x,y) pixel value from a returned WMS image. This is easier to use for a naive client that is not able to perform true geographic referencing.

The standard parameters for the GetFeatureInfo operation are:

Parameter Required? Description
service Yes Service name. Value is WMS.
version Yes Service version. Value is one of 1.0.0, 1.1.0, 1.1.1, 1.3.
request Yes Operation name. Value is GetFeatureInfo.
layers Yes See GetMap
styles Yes See GetMap
srs or crs Yes See GetMap
bbox Yes See GetMap
width Yes See GetMap
height Yes See GetMap
query_layers Yes Comma-separated list of one or more layers to query.
info_format No Format for the feature information response. See below for values.
feature_count No Maximum number of features to return. Default is 1.
x or i Yes X ordinate of query point on map, in pixels. 0 is left side. i is the parameter key used in WMS 1.3.0.
y or j Yes Y ordinate of query point on map, in pixels. 0 is the top. j is the parameter key used in WMS 1.3.0.
exceptions No Format in which to report exceptions. The default value is application/vnd.ogc.se_xml.

Geoserver supports a number of output formats for the GetFeatureInfo response. Server-styled HTML is the most commonly-used format. For maximum control and customisation the client should use GML3 and style the raw data itself. The supported formats are:

Format Syntax Notes
TEXT info_format=text/plain Simple text output. (The default format)
GML 2 info_format=application/vnd.ogc.gml Works only for Simple Features (see Complex Features)
GML 3 info_format=application/vnd.ogc.gml/3.1.1 Works for both Simple and Complex Features (see Complex Features)
HTML info_format=text/html Uses HTML templates that are defined on the server. See GetFeatureInfo Templates for information on how to template HTML output.
JSON info_format=application/json Simple Json representation.
JSONP info_format=text/javascript Returns a JsonP in the form: parseResponse(...json...). See WMS vendor parameters to change the callback name. Note that this format is disabled by default (See Global variables affecting WMS).

GeoServer provides the following vendor-specific parameters for the GetFeatureInfo operation. They are fully documented in the WMS vendor parameters section.

Parameter Required? Description
buffer No width of search radius around query point.
cql_filter No Filter for returned data, in ECQL format
filter No Filter for returned data, in OGC Filter format
propertyName No Feature properties to be returned

An example request for feature information from the topp:states layer in HTML format is:

http://localhost:8080/geoserver/wms?
request=GetFeatureInfo
&service=WMS
&version=1.1.1
&layers=topp%3Astates
&styles=
&srs=EPSG%3A4326
&format=image%2Fpng
&bbox=-145.151041%2C21.73192%2C-57.154894%2C58.961059
&width=780
&height=330
&query_layers=topp%3Astates
&info_format=text%2Fhtml
&feature_count=50
&x=353
&y=145
&exceptions=application%2Fvnd.ogc.se_xml

An example request for feature information in GeoJSON format is:

http://localhost:8080/geoserver/wms?
&INFO_FORMAT=application/json
&REQUEST=GetFeatureInfo
&EXCEPTIONS=application/vnd.ogc.se_xml
&SERVICE=WMS
&VERSION=1.1.1
&WIDTH=970&HEIGHT=485&X=486&Y=165&BBOX=-180,-90,180,90
&LAYERS=COUNTRYPROFILES:grp_administrative_map
&QUERY_LAYERS=COUNTRYPROFILES:grp_administrative_map
&TYPENAME=COUNTRYPROFILES:grp_administrative_map

The result will be:

{
"type":"FeatureCollection",
"features":[
   {
      "type":"Feature",
      "id":"dt_gaul_geom.fid-138e3070879",
      "geometry":{
         "type":"MultiPolygon",
         "coordinates":[
            [
               [
                  [
                     XXXXXXXXXX,
                     XXXXXXXXXX
                  ],
                  ...
                  [
                     XXXXXXXXXX,
                     XXXXXXXXXX
                  ]
               ]
            ]
         ]
      },
      "geometry_name":"at_geom",
      "properties":{
         "bk_gaul":X,
         "at_admlevel":0,
         "at_iso3":"XXX",
         "ia_name":"XXXX",
         "at_gaul_l0":X,
         "bbox":[
            XXXX,
            XXXX,
            XXXX,
            XXXX
         ]
      }
   }
],
"crs":{
   "type":"EPSG",
   "properties":{
      "code":"4326"
   }
},
"bbox":[
   XXXX,
   XXXX,
   XXXX,
   XXXX
]
}

DescribeLayer

The DescribeLayer operation is used primarily by clients that understand SLD-based WMS. In order to make an SLD one needs to know the structure of the data. WMS and WFS both have operations to do this, so the DescribeLayer operation just routes the client to the appropriate service.

The standard parameters for the DescribeLayer operation are:

Parameter Required? Description
service Yes Service name. Value is WMS.
version Yes Service version. Value is 1.1.1.
request Yes Operation name. Value is DescribeLayer.
layers Yes See GetMap
exceptions No Format in which to report exceptions. The default value is application/vnd.ogc.se_xml.

Geoserver supports a number of output formats for the DescribeLayer response. Server-styled HTML is the most commonly-used format. The supported formats are:

Format Syntax Notes
TEXT output_format=text/xml Same as default.
GML 2 output_format=application/vnd.ogc.wms_xml The default format.
JSON output_format=application/json Simple Json representation.
JSONP output_format=text/javascript Return a JsonP in the form: paddingOutput(...jsonp...). See WMS vendor parameters to change the callback name. Note that this format is disabled by default (See Global variables affecting WMS).

An example request in XML (default) format on a layer is:

http://localhost:8080/geoserver/topp/wms?service=WMS
&version=1.1.1
&request=DescribeLayer
&layers=topp:coverage
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE WMS_DescribeLayerResponse SYSTEM "http://localhost:8080/geoserver/schemas/wms/1.1.1/WMS_DescribeLayerResponse.dtd">
<WMS_DescribeLayerResponse version="1.1.1">
   <LayerDescription name="topp:coverage" owsURL="http://localhost:8080/geoserver/topp/wcs?" owsType="WCS">
      <Query typeName="topp:coverage"/>
   </LayerDescription>
</WMS_DescribeLayerResponse>

An example request for feature description in JSON format on a layer group is:

http://localhost:8080/geoserver/wms?service=WMS
&version=1.1.1
&request=DescribeLayer
&layers=sf:roads,topp:tasmania_roads,nurc:mosaic
&outputFormat=application/json

The result will be:

{
version: "1.1.1",
layerDescriptions: [
{
   layerName: "sf:roads",
   owsURL: "http://localhost:8080/geoserver/wfs/WfsDispatcher?",
   owsType: "WFS",
   typeName: "sf:roads"
},
{
   layerName: "topp:tasmania_roads",
   owsURL: "http://localhost:8080/geoserver/wfs/WfsDispatcher?",
   owsType: "WFS",
   typeName: "topp:tasmania_roads"
},
{
   layerName: "nurc:mosaic",
   owsURL: "http://localhost:8080/geoserver/wcs?",
   owsType: "WCS",
   typeName: "nurc:mosaic"
}
]
}

GetLegendGraphic

The GetLegendGraphic operation provides a mechanism for generating legend graphics as images, beyond the LegendURL reference of WMS Capabilities. It generates a legend based on the style defined on the server, or alternatively based on a user-supplied SLD. For more information on this operation and the various options that GeoServer supports see GetLegendGraphic.