1. Google Maps.
https://maps.google.com/
2. Yahoo! Maps.
http://map.yahoo.co.jp/
3. Thomson, R.C., Richardson, D.E.: ‘Good continuation’ principle of perceptual organization applied to the generalization of road networks. In: Proceedings of the 19th International Cartographic Conference (ICC), pp. 1215–1223 (1999)
4. Zhang, Q.: Road network generalization based on connection analysis. In: Development in Spatial Data Handling 2005, pp. 343-353 (2005)
5. Fujii, K., Sugiyama, K.: Route Guide Map Generation System for Mobile Communication. Information Processing Society of Japan (IPSJ) Journal 41(9), 2394–2403 (2000)