Based on building polygons (building footprints) on a digital map, a GIS and CG integrated system to generate 3D
building models automatically is proposed. Most building polygons' edges meet at right angles (orthogonal polygon). A
complicated orthogonal polygon can be partitioned into a set of rectangles. In order to partition an orthogonal polygon,
we proposed a useful polygon expression (RL expression) and a partitioning scheme in deciding from which vertex a
dividing line (DL) is drawn. After partitioning, the integrated system will place rectangular roofs and box-shaped
building bodies on these rectangles. In this paper, we propose a new scheme for partitioning building polygons and for
creating a complicated shape of building models based on orthogonal building polygons.