[[geohash-prefix]]
=== `geohash_prefix`

Geohashes are a form of lat/lon encoding which divides the earth up into
a grid. Each cell in this grid is represented by a geohash string. Each
cell in turn can be further subdivided into smaller cells which are
represented by a longer string. So the longer the geohash, the smaller
(and thus more accurate) the cell is.

While the <<geohash,`geohash`>> option enables indexing the geohash that
corresponds to the lat/lon point, at the specified
<<geohash-precision,precision>>, the `geohash_prefix` option will also
index all the enclosing cells as well.

For instance, a geohash of `drm3btev3e86` will index all of the following
terms: [ `d`, `dr`, `drm`, `drm3`, `drm3b`, `drm3bt`, `drm3bte`, `drm3btev`,
`drm3btev3`, `drm3btev3e`, `drm3btev3e8`, `drm3btev3e86` ].

The geohash prefixes can be used with the
<<query-dsl-geohash-cell-query,`geohash_cell` query>> to find points within a
particular geohash, or its neighbours:


[source,js]
--------------------------------------------------
PUT my_index
{
  "mappings": {
    "my_type": {
      "properties": {
        "location": {
          "type": "geo_point",
          "geohash_prefix": true,
          "geohash_precision": 6
        }
      }
    }
  }
}

PUT my_index/my_type/1
{
  "location": {
    "lat": 41.12,
    "lon": -71.34
  }
}

GET my_index/_search?fielddata_fields=location.geohash
{
  "query": {
    "geohash_cell": {
      "location": {
        "lat": 41.02,
        "lon": -71.48
      },
      "precision": 4, <1>
      "neighbors": true <1>
    }
  }
}
--------------------------------------------------
// AUTOSENSE