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GHAM: A Compact Global Geocode Suitable for Sorting

Duncan C. Agnew

Published October 2005, SCEC Contribution #865

The GHAM code is a technique for labeling geographic locations based on their positions. It defines addresses for equal-area cells bounded by constant latitude and longitude, with arbitrarily fine precision. The cell codes are defined by applying Morton ordering to a recursive division into a 16 by 16 grid, with the resulting numbers encoded into letter–number pairs. A lexical sort of lists of points so labeled will bring near neighbors (usually) close together; tests on a variety of global datasets show that in most cases the actual closest point is adjacent in the list 50% of the time, and within 5 entries 80% of the time.

Agnew, D. C. (2005). GHAM: A Compact Global Geocode Suitable for Sorting. Computers and Geosciences, 31(8), 1042-1047. doi: 10.1016/j.cageo.2005.02.007.