A method of updating information stored in an index associated with spatially-related objects. The method includes accessing a hierarchical multi-level index having leaf nodes containing information about an object and non-leaf nodes storing information about a number of nodes related to the non-leaf...http://www.google.com.hk/patents/US8190649?utm_source=gb-gplus-share專利 US8190649 - Ranking and clustering of geo-located objects
