A FORTRAN SUBROUTINE FOR CARTOGRAPHIC GENERALIZATION

In this paper a FORTRAN subroutine for the generalization of the topological structure of topographic surfaces is presented. The surface topology is characterized by weighted surface networks (Pfaltz-graphs) which represent special types of graphs with the vertex sets consisting of the critical or so-called surface-specific points (pits, passes, peaks) and the edge sets consisting of the critical or so-called surface-specific lines (ridges, courses) of the corresponding topographic surfaces: in addition, real numbers greater than zero are associated with the edges and vertices in order to indicate their importance for the macro- and microstructure of the underlying surface. The so-defined weighted surface networks can be condensed by two graph-theoretic contractions which reduce the number of edges and nodes but preserve the topological structure of the associated Pfaltz-graphs and consequently that of the corresponding topographic surfaces; thus the two contractions are equivalent to elementary steps of a cartographic generalization process. The procedure presented in this article is the FORTRAN equivalent of an algorithm resting on these two contractions and thus being able to condense a given topographic surface until a specified degree of simplicity is achieved.