Problems Arising From A Simple GIS Generalisation Algorithm

Practical GIS generalisation using existing Arc/Info operations invariably follows a simple, generic generalisation algorithm. Typically the algorithm consists of dissolving adjacent polygons with the same attribute value, line generalisation, selection of all polygons of small area, and elimination of selected polygons by merging with the neighbouring polygon of largest area. This paper addresses two fundamental problems with this simple algorithm: performing topologically consistent line generalisation that preserves polygon adjacencies; and establishing criteria and operators for selection of polygons as candidates for elimination. In particular, we consider the utility of the polygon skeleton in each of these contexts. These problems arose in attempts to reproduce a generalised Soil Map of New Zealand from higher resolution soils polygons of the New Zealand Land Resource Inventory. We have developed additional tools that operate on existing Arc/Info coverages and contribute further generalisation logic.