Spatial Extent Models for Natural Language Phrases Involving Directional Containment

We study the problem of assigning a spatial extent to a text phrase such as central northern California', with the objective of allowing spatial interpretations of natural language, and consistency testing of complex utterances that involve multiple phrases from which spatial extent can be derived. The work presented addresses alternative spatial extent assignations, and the evaluation of those alternatives to decide on the best performing ones. Three important classes of these phrases are identified and we call them full direction phrases, half-direction phrases, and extreme direction phrases, respectively. Examples of these are: north-western California', central northern California', and extreme south-eastern California'. Such descriptions vaguely delineate a spatial extent, and we attempt to derive a region-representation for them. Our approach is to identify a number of extent assignation parameters, which are used to derive a variety of spatial extent models, each of which we evaluate against a large gazetteer corpus. Three example assignation parameters used are: choice of center, choice of shape of central sector, and choice of shape of outer sectors. The corpus used for the evaluation is the two-volume Ornithological Gazetteer of Brazil (Paynter and Traylor 1991a, b). It allows us to compare the spatial extent assignations and derive recommendations for such assignations for future use