Semantics, Metadata, Geographical Information and Users.

Semantics is concerned with analysing the meaning encoded in language (Calvani, 2004). Within a technical description of data, semantic descriptions ought to be an important adjunct, filling out the labels and codings of classes and providing justification for measurements. Semantics is equally applicable whether applied to single word labels (Building, Tree etc.), short phrases (coniferous forest, upland moors, etc.), or to longer textual descriptions of a phenomenon. Data semantics also includes the general description of a dataset and its characteristics and limitations. Spatial data and their semantics vary for a variety of reasons that are not to do with differences in the feature being measured. In the creation of any spatial data there are a series of choices about what to map and how to map it which will depend on a range of commissioning and institutional factors. Different choices result in different representations and variation between datasets. The variability between different, but equally valid, mappings of the same real world objects ultimately points to the social construction of spatial data (Harvey and Chrisman, 1998). Much valuable geographical information is therefore embedded in its semantics.