Journal of Architecture and Planning (Transactions of AIJ)
Online ISSN : 1881-8161
Print ISSN : 1340-4210
ISSN-L : 1340-4210
FORMULATION OF AN INDICATOR OF CENTRALITY THAT CONSIDERS TRIP GENERATION AS WELL AS TRIP DISTANCE AND COMPARISON WITH INDICATORS USING GRAPH THEORY
Takuro KOJOTohru YOSHIKAWA
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2021 Volume 86 Issue 785 Pages 1948-1959

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Abstract

This article aims at proposing an indicator of centrality that consider a trip generation and trip distance in cities and at clarifying its expressibility by comparison with betweenness centrality and advantage of position.

Historically cities have been recognized to have centrality. Research on the centrality of cities has been conducted for a long time, such as the central place theory by Christaller and Lösch. However, the theory assumes that the center is in a given position, and it cannot explain that a specific location is the center. On the other hand, using graph theory, we can obtain an indicator of centrality in cities by considering the road network as a network. Among them, betweenness centrality and advantage of position are mentioned as typical indicators. However, the relationship between these indicators and travel behavior, an important background of centrality, is not clear. To fill this research gap, we formulate a simple indicator that takes trip into account and clarify its expressibility by comparison between the formulated indicator and the existing ones in a virtual city with grid street networks.

The indicator, which represents the location potential, is defined as follows. People leave our homes, do some activities near their homes, and go home. The farther they are from home, the lower their probability of going by an exponential function. We assume that their numbers of trips are uniform and are proportionally allocated according to the accessibility to each destination. From the viewpoint of the destination side, the accumulated numbers of the trips can be interpreted as the location potential of urban facility and they are higher in the place where many people we can easily go. We also assume that the population density in the virtual city is uniform, and thus the trip generation quantity of each district is also uniform.

The results are as follows. In a society where long-distance trips are difficult in such cases as the car ownership rate is low or people are old, the potential tends to be uniform. In contrast, in a society where the difficulty in travel is low in such cases as the car ownership rate rises, the potential of the central place where everyone can easily go rises. If facilities for people of all ages are located in the geometrical center of the city, they can easily attract customers, but facilities for the elderly can hardly attract customers there. Furthermore, when the difficulty in travel decreases more than a certain level, the centrality of the geometrical center of the city falls and the regional difference in the centrality became smaller. The interpretation of the parameters can also express differences in location possibilities due to the order of goods and services.

The results also show that the location potential can approximate the centrality distribution of the betweenness centrality and advantage of position, by adjustment of the parameters. It is also found that the betweenness centrality is very similar to the advantage of position. The absolute values of the location potential are different from these indicators, while the magnitude relation of the relative value is similar to them. It suggests that the location potential can express various centralities according to the city size, means of transportation, and facilities for various age groups by adjusting the parameters to the actual travel behavior.

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© 2021, Architectural Institute of Japan
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