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Defining and Generating Axial Lines from Street Center Lines for better Understanding of Urban Morphologies
Axial lines are defined as the longest visibility lines for representing
individual linear spaces in urban environments. The least number of axial lines
that cover the free space of an urban environment or the space between
buildings constitute what is often called an axial map. This is a fundamental
tool in space syntax, a theory developed by Bill Hillier and his colleagues for
characterizing the underlying urban morphologies. For a long time, generating
axial lines with help of some graphic software has been a tedious manual
process that is criticized for being time consuming, subjective, or even
arbitrary. In this paper, we redefine axial lines as the least number of
individual straight line segments mutually intersected along natural streets
that are generated from street center lines using the Gestalt principle of good
continuity. Based on this new definition, we develop an automatic solution to
generating the newly defined axial lines from street center lines. We apply
this solution to six typical street networks (three from North America and
three from Europe), and generate a new set of axial lines for analyzing the
urban morphologies. Through a comparison study between the new axial lines and
the conventional or old axial lines, and between the new axial lines and
natural streets, we demonstrate with empirical evidence that the newly defined
axial lines are a better alternative in capturing the underlying urban
structure.
Keywords: Space syntax, street networks, topological analysis, traffic,
head/tail division ruleComment: 10 pages, 7 figures, and 2 tables, one figure added + minor revisio
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