Multicell quad trees

The multicell quad tree is a two-level tree structure for region queries. At the upper level is a multiple storage quad tree (MSQT). At the lower level, each leaf quad of the MSQT is further subdivided into equal-sized cells. Basically, large-window queries examine structures at the coarse-grained leaf quad level while small-window queries examine structures at the fine-grained cell level. With such two-level structures fitting each kind of queries separately, both large-window and small-window queries can achieve high execution speeds