Leonardo Guerreiro Azevedo Geraldo Zimbrão Jano Moreira de Souza Approximate Query Processing in Spatial Databases Using Raster Signatures. 53-72 2006 conf/geoinfo/2006 GeoInfo http://www.geoinfo.info/geoinfo2006/papers/p20.pdf db/conf/geoinfo/geoinfo2006.html#AzevedoZS06