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+Adds the specified geospatial items (latitude, longitude, name) to the specified
+key. Data is stored into the key as a sorted set, in a way that makes it
+possible to later retrieve items using a query by radius with the `GEORADIUS` or
+`GEORADIUSBYMEMBER` commands.
+
+The command takes arguments in the standard format x,y so the longitude must be
+specified before the latitude. There are limits to the coordinates that can be
+indexed: areas very near to the poles are not indexable. The exact limits, as
+specified by EPSG:900913 / EPSG:3785 / OSGEO:41001 are the following:
+
+- Valid longitudes are from -180 to 180 degrees.
+- Valid latitudes are from -85.05112878 to 85.05112878 degrees.
+
+The command will report an error when the user attempts to index coordinates
+outside the specified ranges.
+
+**Note:** there is no **GEODEL** command because you can use `ZREM` in order to
+remove elements. The Geo index structure is just a sorted set.
+
+## How does it work?
+
+The way the sorted set is populated is using a technique called
+[Geohash](https://en.wikipedia.org/wiki/Geohash). Latitude and Longitude bits
+are interleaved in order to form an unique 52 bit integer. We know that a sorted
+set double score can represent a 52 bit integer without losing precision.
+
+This format allows for radius querying by checking the 1+8 areas needed to cover
+the whole radius, and discarding elements outside the radius. The areas are
+checked by calculating the range of the box covered removing enough bits from
+the less significant part of the sorted set score, and computing the score range
+to query in the sorted set for each area.
+
+## What Earth model does it use?
+
+It just assumes that the Earth is a sphere, since the used distance formula is
+the Haversine formula. This formula is only an approximation when applied to the
+Earth, which is not a perfect sphere. The introduced errors are not an issue
+when used in the context of social network sites that need to query by radius
+and most other applications. However in the worst case the error may be up to
+0.5%, so you may want to consider other systems for error-critical applications.
+
+@return
+
+@integer-reply, specifically:
+
+- The number of elements added to the sorted set, not including elements already
+  existing for which the score was updated.
+
+@examples
+
+```cli
+GEOADD Sicily 13.361389 38.115556 "Palermo" 15.087269 37.502669 "Catania"
+GEODIST Sicily Palermo Catania
+GEORADIUS Sicily 15 37 100 km
+GEORADIUS Sicily 15 37 200 km
+```