1. Google maps. https://www.google.co.jp/maps. Google maps. https://www.google.co.jp/maps.
2. Yahoo! maps maps. http://map.yahoo.co.jp/. Yahoo! maps maps. http://map.yahoo.co.jp/.
3. Google street view. https://www.google.com/streetview/. Google street view. https://www.google.com/streetview/.
4. Bing maps. https://www.bing.com/maps/. Bing maps. https://www.bing.com/maps/.
5. A model for detailed binary topological relationships;Egenhofer J.M.;Geomatica,1993