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The first step is to decide just how much precision you need.
Although you could
index all geo-points with the default full 12 levels of precision, do you
really need to be accurate to within a few centimeters? You can save yourself
a lot of space in the index by reducing your precision requirements to
something more realistic, such as
The precision can be specified as an absolute number, representing the
length of the geohash, or as a distance. A precision of
With this mapping in place, geohash prefixes of lengths 1 to 7 will be indexed, providing geohashes accurate to about 150 meters.