Voronoi-based region approximation for geographical information retrieval with gazetteers

Gazeteers and geographical thesauri can be regarded as parsimonious spatial models that associate geographical location with place names and encode so me semantic relations between the names. They are of particular value in pr ocessing information retrieval requests in which the user employs place nam es to specify geographical context. Typically the geometric locational data in a gazetteer are confined to a simple footprint in the form of a centroi d or a minimum bounding rectangle, both of which can be used to link to a m ap but are of limited value in determining spatial relationships. Here we d escribe a Voronoi diagram method for generating approximate regional extent s from sets of centroids that are respectively inside and external to a reg ion. The resulting approximations provide measures of areal extent and can be used to assist in answering geographical queries by evaluating spatial r elationships such as distance, direction and common boundary length. Prelim inary experimental evaluations of the method have been performed in the con text of a semantic modelling system that combines the centroid data with hi erarchical and adjacency relations between the associated place names.