ABSTRACT

In a GIS context, a categorical thematic map is a topologically-ordered collection of spatial entities (points, lines, polygons, cells) in which descriptors about a theme (usually defined within a discrete classification scheme) are given spatial extent, location and boundary so that within-unit variation is expected to be less than between-unit variation, where a unit is a polygon or contiguous group of cells having a common descriptor. Thematic maps, whether in analog or digital form, have an unavoidable characteristic : uncertainty.