Create a 2d Index
To build a geospatial 2d index, use the
db.collection.createIndex() method and specify 2d. Use the
following syntax:
db.<collection>.createIndex( { <location field> : "2d" , <additional field> : <value> } , { <index-specification options> } )
The 2d index uses the following optional index-specification
options:
{ min : <lower bound> , max : <upper bound> , bits : <bit precision> }
Define Location Range for a 2d Index
By default, a 2d index assumes longitude and latitude and has boundaries
of -180 inclusive and 180 non-inclusive. If
documents contain coordinate data outside of the specified range,
MongoDB returns an error.
Important
The default boundaries allow applications to insert documents with invalid latitudes greater than 90 or less than -90. The behavior of geospatial queries with such invalid points is not defined.
On 2d indexes you can change the location range.
You can build a 2d geospatial index with a location range other than
the default. Use the min and max options when creating the
index. Use the following syntax:
db.collection.createIndex( { <location field> : "2d" } , { min : <lower bound> , max : <upper bound> } )
Define Location Precision for a 2d Index
By default, a 2d index on legacy coordinate pairs uses 26 bits of
precision, which is roughly equivalent to 2 feet or 60 centimeters of
precision using the default range of -180 to 180. Precision is measured
by the size in bits of the geohash values used to store location
data. You can configure geospatial indexes with up to 32 bits of
precision.
Index precision does not affect query accuracy. The actual grid coordinates are always used in the final query processing. Advantages to lower precision are a lower processing overhead for insert operations and use of less space. An advantage to higher precision is that queries scan smaller portions of the index to return results.
To configure a location precision other than the default, use the
bits option when creating the index. Use following syntax:
db.<collection>.createIndex( {<location field> : "<index type>"} , { bits : <bit precision> } )
For information on the internals of geohash values, see
Calculation of Geohash Values for 2d Indexes.