A Topological Representation for Taking Cities as a Coherent Whole

TL;DR

This paper introduces a topology-based geographic representation of cities as interconnected points within hierarchical networks, enabling analysis of their wholeness and offering new insights for urban design and pattern assessment.

Contribution

It develops a novel topological framework for representing cities as hierarchical networks, contrasting with traditional geometry-based methods, and demonstrates its application through case studies.

Findings

Cities exhibit properties of differentiation and adaptation in their wholeness.

The topological representation effectively captures hierarchical relationships among cities.

Case studies validate the approach using data from China and UK cities.

Abstract

A city is a whole, as are all cities in a country. Within a whole, individual cities possess different degrees of wholeness, defined by Christopher Alexander as a life-giving order or simply a living structure. To characterize the wholeness and in particular to advocate for wholeness as an effective design principle, this paper develops a geographic representation that views cities as a whole. This geographic representation is topology-oriented, so fundamentally differs from existing geometry-based geographic representations. With the topological representation, all cities are abstracted as individual points and put into different hierarchical levels, according to their sizes and based on head/tail breaks - a classification scheme and visualization tool for data with a heavy tailed distribution. These points of different hierarchical levels are respectively used to create Thiessen polygons. Based on polygon-polygon relationships, we set up a complex network. In this network, small polygons point to adjacent large polygons at the same hierarchical level and contained polygons point to containing polygons across two consecutive hierarchical levels. We computed the degrees of wholeness for individual cities, and subsequently found that the degrees of wholeness possess both properties of differentiation and adaptation. To demonstrate, we developed four case studies of all China and UK natural cities, as well as Beijing and London natural cities, using massive amounts of street nodes and Tweet locations. The topological representation and the kind of topological analysis in general can be applied to any design or pattern, such as carpets, Baroque architecture and artifacts, and fractals in order to assess their beauty, echoing the introductory quote from Christopher Alexander. Keywords: Wholeness, natural cities, head/tail breaks, complex networks, scaling hierarchy, urban design