Seismic microzonation maps are very useful materials for prevention of earthquake disaster at a site. It is needed to investigate mesh-size of the map which is appropriate for topographies of small islands like Okinawa prefecture. But larger number of meshes requires the more data of subsurface layers at the site. It seems to be the most probable that there are not enough of the necessary data. This study proposes a practical method, which can supplement shortage of the data, by using statistical analysis for available data on geomorphological land classification and geological survey. Furthermore, based on the supplemented data, a practical formula estimating dynamic physical properties of surface layers in Okinawa prefecture is proposed.