According to the Building Standards Law, lots have to be basically adjacent to a road whose width is equal to or more than 4 meters. Due to spatial data limitation, it is impossible to judge if a lot is adjacent to a road defined above by using Geographical Information Systems (GIS) in general. Meanwhile, there are many spatial data of buildings available. The principal, that each building is basically built on a lot, potentially enables us to judge indirectly if a lot is adjacent to a road. There are mainly two methods to do this: the method using buffer polygons and the method using Voronoi segmentations. The accuracy of these methods to judge adjacency of a lot to a road is examined. It is shown that the difference of the degree of accuracy between them is from 0.2% to 3.3%, implying that the method using buffer polygon is a practical substitution for the method using Voronoi segmentation in view of time required.
