PostGIS
Description
Return a GeoHash representation (http://en.wikipedia.org/wiki/Geohash) of the geometry. A GeoHash encodes a point into a text form that is sortable and searchable based on prefixing. A shorter GeoHash is a less precise representation of a point. It can also be thought of as a box, that contains the actual point.
If no maxchars is specified ST_GeoHash returns a GeoHash based on
full precision of the input geometry type. Points return a GeoHash with
20 characters of precision (about enough to hold the full double
precision of the input). Other types return a GeoHash with a variable
amount of precision, based on the size of the feature. Larger features
are represented with less precision, smaller features with more
precision. The idea is that the box implied by the GeoHash will always
contain the input feature.
If maxchars is specified ST_GeoHash returns a GeoHash with at most
that many characters so a possibly lower precision representation of the
input geometry. For non-points, the starting point of the calculation is
the center of the bounding box of the geometry.
Availability: 1.4.0
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This method
supports Circular Strings and Curves
Examples
SELECT ST_GeoHash(ST_SetSRID(ST_Point(-126,48),4326));
st_geohash
----------------------
c0w3hf1s70w3hf1s70w3
SELECT ST_GeoHash(ST_SetSRID(ST_Point(-126,48),4326),5);
st_geohash
------------
c0w3h