PolySimp: A Tool for Polygon Simplification Based on the Underlying Scaling Hierarchy

Abstract

Map generalization is a process of reducing the contents of a map or data to properly show a geographic feature(s) at a smaller extent. Over the past few years, the fractal way of thinking has emerged as a new paradigm for map generalization. A geographic feature can be deemed as a fractal given the perspective of scaling, as its rough, irregular, and unsmooth shape inherently holds a striking scaling hierarchy of far more small elements than large ones. The pattern of far more small things than large ones is a de facto heavy tailed distribution. In this paper, we apply the scaling hierarchy for map generalization to polygonal features. To do this, we firstly revisit the scaling hierarchy of a classic fractal: the Koch Snowflake. We then review previous work that used the Douglas–Peuker algorithm, which identifies characteristic points on a line to derive three types of measures that are long-tailed distributed: the baseline length (d), the perpendicular distance to the baseline (x), and the area formed by x and d (area). More importantly, we extend the usage of the three measures to other most popular cartographical generalization methods; i.e., the bend simplify method, Visvalingam–Whyatt method, and hierarchical decomposition method, each of which decomposes any polygon into a set of bends, triangles, or convex hulls as basic geometric units for simplification. The different levels of details of the polygon can then be derived by recursively selecting the head part of geometric units and omitting the tail part using head/tail breaks, which is a new classification scheme for data with a heavy-tailed distribution. Since there are currently few tools with which to readily conduct the polygon simplification from such a fractal perspective, we have developed PolySimp, a tool that integrates the mentioned four algorithms for polygon simplification based on its underlying scaling hierarchy. The British coastline was selected to demonstrate the tool’s usefulness. The developed tool can be expected to showcase the applicability of fractal way of thinking and contribute to the development of map generalization.

Automatic Generalization of Residential Areas Based on “Paradigm” Theory and Big Data

“…However, there are still many problems worthy of study in this field. The key is feature extraction, especially automatic feature extraction to reduce manual annotation [13][14].…”

Geographic Complexity: Concepts, Theories, and Practices

“…More importantly, they found that the fractality of street networks is positively correlated with urban socioeconomic status and negatively correlated with energy consumption. In another study, Ma et al [22] developed a useful tool, called PolySimp, for simplifying complex polygons based on the underlying scaling hierarchy of polygons. The tool's effectiveness has been demonstrated using British coastline data.…”