PostGIS and MySQL use R-Tree indexes, which are rather specifically for spatial data (well, any data type which can be decomposed to a range rectangle). So does Oracle Spatial, for that matter. Space-filling curves, which map multi-dimensional data to something sortable into a B-Tree are ways of leveraging non-spatial database technology to be more useful for spatial data. Space-filling technicques tend not to be as balanced as R-Trees, however. The heirarchical grid is the final trick, and can be quite performant, but needs to be carefully tuned to the characteristics of the data, unlike R-Trees which automagically work for data of uneven scales.

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PostGIS and MySQL use R-Tree indexes, which are rather specifically for spatial data (well, any data type which can be decomposed to a range rectangle). So does Oracle Spatial, for that matter. Space-filling curves, which map multi-dimensional data to something sortable into a B-Tree are ways of leveraging non-spatial database technology to be more useful for spatial data. Space-filling technicques tend not to be as balanced as R-Trees, however. The heirarchical grid is the final trick, and can be quite performant, but needs to be carefully tuned to the characteristics of the data, unlike R-Trees which automagically work for data of uneven scales.

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