116 3 Non-geometry standards
browser. A great variety of maps or other visual representations of geodata have already become available on the Internet. A Web Map Service produces maps of georeferenced data. In this context, a map is a visual representation of geodata but it is
not the data itself. The ISO 19128 (Web Map server interface) is a specification that
standardises the way maps are requested by clients via the Internet and the way that
serverS describe their data holdings. The ISO 19128 is a web interface specification
for mapping data.
Originally, the ISO standard "Web Map server interface" was a development of
the Open GIS Consortiurn (OGC) (De La Beaujardiere 2002).
Operations
The ISO standard "Web Map server interface" defines three operations, the first
two of which are required of every Web Map server.
• Get Capabilities (required): Obtain service-level metadata that is a machinereadable (and human-readable) description of the Web Map server's information content and acceptable request parameters.
• GetMap (required): Obtain a map image for which the geospatial and dimensional parameters are weIl defined.
• GetFeatureInfo (optional): Ask for information about particular features shown
on amap.
Processing
A standard web browser can ask a Web Map server to perform these operations
by simply submitting requests in the form of Uniform Resource Locators. When invoking the operation GetMap, a Web Map server client can specify the information
to be shown on the map. Some of the information that could be specified would include the number of layers, the "styles" of those layers, what portion of the earth is
to be mapped (a "bounding box"), the projected or Coordinate Reference System to
be used, the desired output format, the output size (width and height), and the background transparency and colour. When invoking GetFeatureInfo the client indicates
what map is being queried and which location on the map is of interest.
According to the philosophy of the Internet, no main server is responsible for collecting the data requested by the client. The display data commonly reside only at the
client's computer. A particular Web Map server provider in a distributed Web Map
server network needs only to be the steward of its own data collection.
Because each Web Map server is independent, a Web Map server must be able to
provide a machine-readable description of its capabilities. The "service metadata"
enables clients to formulate valid requests and enables the construction of searchable
catalogues that can direct clients to particular Web Map services.
A Web Map service may optionally allow the GetFeatureInfo operation. If it does,
its maps are said to be "queryable", and a client can request information about features on the map by adding a position around which nearby features are searched for.
browser. A great variety of maps or other visual representations of geodata have already become available on the Internet. A Web Map Service produces maps of georeferenced data. In this context, a map is a visual representation of geodata but it is
not the data itself. The ISO 19128 (Web Map server interface) is a specification that
standardises the way maps are requested by clients via the Internet and the way that
serverS describe their data holdings. The ISO 19128 is a web interface specification
for mapping data.
Originally, the ISO standard "Web Map server interface" was a development of
the Open GIS Consortiurn (OGC) (De La Beaujardiere 2002).
Operations
The ISO standard "Web Map server interface" defines three operations, the first
two of which are required of every Web Map server.
• Get Capabilities (required): Obtain service-level metadata that is a machinereadable (and human-readable) description of the Web Map server's information content and acceptable request parameters.
• GetMap (required): Obtain a map image for which the geospatial and dimensional parameters are weIl defined.
• GetFeatureInfo (optional): Ask for information about particular features shown
on amap.
Processing
A standard web browser can ask a Web Map server to perform these operations
by simply submitting requests in the form of Uniform Resource Locators. When invoking the operation GetMap, a Web Map server client can specify the information
to be shown on the map. Some of the information that could be specified would include the number of layers, the "styles" of those layers, what portion of the earth is
to be mapped (a "bounding box"), the projected or Coordinate Reference System to
be used, the desired output format, the output size (width and height), and the background transparency and colour. When invoking GetFeatureInfo the client indicates
what map is being queried and which location on the map is of interest.
According to the philosophy of the Internet, no main server is responsible for collecting the data requested by the client. The display data commonly reside only at the
client's computer. A particular Web Map server provider in a distributed Web Map
server network needs only to be the steward of its own data collection.
Because each Web Map server is independent, a Web Map server must be able to
provide a machine-readable description of its capabilities. The "service metadata"
enables clients to formulate valid requests and enables the construction of searchable
catalogues that can direct clients to particular Web Map services.
A Web Map service may optionally allow the GetFeatureInfo operation. If it does,
its maps are said to be "queryable", and a client can request information about features on the map by adding a position around which nearby features are searched for.