Abstract
Monitoring of the spatial distribution of vacant houses across broad areas by local governments requires substantial labor, time, and money because the main survey method involves visual checks via field surveys. This is a major obstacle for local governments when developing means to measure the number of vacant houses. Therefore, we developed a method for estimating the spatial distribution of vacant houses using varied spatial data and sample field surveys of part of the target area instead of a field survey of the whole target area to reduce the cost and labor required for the vacant house survey. The target area was the city center of Kagoshima city, Kagoshima Prefecture, shown in Fig. 1.
In chapter 2, we detected the spatial distribution of vacant houses via field surveys according to the criteria for vacant and non-vacant houses shown in Table 3. This was conducted in sample field survey areas that contained 3, 134 detached buildings, shown in Fig. 1 and in Table 2. Table 4 shows the results of the field survey in the sample field survey areas. The table shows that there are 173 detached vacant houses in these areas.
In chapter 3, we developed the vacant house database to first integrate the results of the field survey, digital residential map, and municipal public data that included the basic resident register, closed hydrant information, and the building registration information. Second, we calculated the number of vacant houses and rates of building use for detached buildings based on the presence or absence of public data using the vacant house database shown in Table 5. The number of vacant houses in each 500m square grid could be estimated by applying these values. Finally, we calculated vacant house scores for all of the detached buildings based on Table 6. Detached buildings were assigned as vacant houses in descending order of the vacant house score until meeting the number of vacant house by 500m square grids. Scores tended to be larger for smaller numbers of people per household and building area, larger proportions of older residents, the maximum and minimum duration of residence, and earlier construction year. Using this method, the spatial distribution of vacant houses in the target area could be estimated. In addition, we verified the reliability of our method. We compared the number of actual vacant houses monitored by field surveys in the sample field survey areas with the estimated number of vacant houses calculated by our method, accumulated within 500m square and 250m square grids. Table 7 shows the comparison results for the case of a 500m square grid and Table 8 the case of a 250m square grid. Both set of results showed that there were no significant differences between actual values and our estimated values. This indicates that the method proposed in this study can estimate the spatial distribution of vacant houses with good accuracy.
Chapter 4 introduced the results for the estimation of the spatial distribution of vacant house in the target area i.e. the city center of Kagoshima city. Fig. 4 to Fig. 7 show the estimated results of the number of vacant houses and rates aggregated into 500m square grids and city blocks. The results estimated that 1,740 detached buildings were vacant of the 32,448 detached buildings in the target area, i.e. 5.36% of houses were vacant. Our method can estimate the number of vacant houses and their rates to aggregate them into spatial units according to the objective.
