Automated Cartographic Generalization For Linear Features

An automated method is presented for the generalization of linear features that are already in a topologically structured computer-readable form. The method consists of three stages: feature elimination; feature simplification; and interference detection and resolution. The first stage is implemented using English-like rules to specify which map features are to be eliminated at the generalized map scale. The second stage consists of the simplification of linear map features, specifically in the form of polyline simplification and riverbank combination. The third stage deals with interference detection and resolution among linear map features. Due to the width of the symbol representing a feature, interference may occur when a simplified feature is added to the generalized map and it overlaps another feature already on the generalized map. If that occurs, one or both of the interfering features have to be displaced so as to eliminate the interference between them. This displacement may cause other features to be subsequently displaced in a process called feature displacement propagation. The algorithms used to detect feature interference and to perform the subsequent feature displacement propagation are described. A FORTRAN 77 computer program called MAPEX was written to perform automated generalization of linear map features. The intended scale range for MAPEX is 1:24 000 to 1: 250 000. The results of running MAPEX on two topologically structured test data files are given, along with some of the algorithmic details used in the implementation of the program.