In large scale earth observation systems, data is gathered in short duration surveys returning massive numbers of point data observations (often millions) covering significantly sized regions. To maintain up-to-date products (e.g. navigation charts in harbours with continuous silt build-up), successive surveys are performed that often cover overlapping areas. Searches to find all the data in a specific region are expected to return only the most recent data in any given area, and must ignore any older, overlapping versions.