V. Guralnik, and J. Srivastava. Proceedings of the fifth ACM SIGKDD international conference on Knowledge discovery and data mining, page 33--42. New York, NY, USA, ACM, (1999)
C. Wang, X. Xie, L. Wang, Y. Lu, and W. Ma. Proceedings of the 2005 workshop on Geographic information retrieval, page 17--24. New York, NY, USA, ACM, (2005)