3. The method of claim 2 , wherein the at least one of the plurality of leaf nodes also contains relevance information about a corresponding spatial location referred to by the document corresponding to that leaf node.
3. The method of claim 2 , wherein the at least one of the plurality of leaf nodes also contains relevance information about a corresponding spatial location referred to by the document corresponding to that leaf node. 4. The method of claim 3 , further comprising constructing the spatial keyword document indexes for the corresponding keyword by: populating the at least one of the plurality of leaf nodes with a copy of the spatial document index with a relevance of that corresponding keyword to the document identified by that leaf node; pruning all unpopulated leaf nodes where the corresponding keyword does not appear in the document identified by that leaf node; and recursively pruning from the bottom up all non-leaf nodes that have no children.