US Patent 9436702 Navigation system data base system

A system for performing a similarity search in a navigation device data base uses a metric index structure. The index structure includes a plurality of nodes. When a query object is received, a node of the index structure which is associated with at least one object is accessed. A distance between the query object and the at least one object is determined in accordance with a distance metric. Based on the determined distance, another node of the index structure is selectively accessed.