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Indexes

2d Indexes

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  • Considerations
  • Behavior
  • sparse Property
  • Collation Option

Use a 2d index for data stored as points on a two-dimensional plane. The 2d index is intended for legacy coordinate pairs used in MongoDB 2.2 and earlier.

Use a 2d index if:

  • your database has legacy legacy coordinate pairs from MongoDB 2.2 or earlier, and

  • you do not intend to store any location data as GeoJSON objects.

For more information on geospatial queries, see Geospatial Queries.

Considerations

Starting in MongoDB 4.0, you can specify a key option to the $geoNear pipeline stage to indicate the indexed field path to use. This allows the $geoNear stage to be used on a collection that has multiple 2d index and/or multiple 2dsphere index:

  • If your collection has multiple 2d index and/or multiple 2dsphere index, you must use the key option to specify the indexed field path to use.

  • If you do not specify the key, you cannot have multiple 2d index and/or multiple 2dsphere index since without the key, index selection among multiple 2d indexes or 2dsphere indexes is ambiguous.

Note

If you do not specify the key, and you have at most only one 2d index and/or only one 2dsphere index, MongoDB looks first for a 2d index to use. If a 2d index does not exists, then MongoDB looks for a 2dsphere index to use.

Do not use a 2d index if your location data includes GeoJSON objects. To index on both legacy coordinate pairs and GeoJSON objects, use a 2dsphere index.

You cannot use a 2d index as a shard key when sharding a collection. However, you can create a geospatial index on a sharded collection by using a different field as the shard key.

Behavior

The 2d index supports calculations on a flat, Euclidean plane. The 2d index also supports distance-only calculations on a sphere (i.e. $nearSphere), but for geometric calculations on a sphere (e.g. $geoWithin), store data as GeoJSON objects and use a 2dsphere index.

A 2d index can reference two fields. The first must be the location field. A 2d compound index constructs queries that select first on the location field, and then filters those results by the additional criteria. A compound 2d index can cover queries.

sparse Property

2d indexes are always sparse and ignore the sparse option. If a document lacks a 2d index field (or the field is null or an empty array), MongoDB does not add an entry for the document to the 2d index. For inserts, MongoDB inserts the document but does not add to the 2d index.

For a compound index that includes a 2d index key along with keys of other types, only the 2d index field determines whether the index references a document.

Collation Option

2d indexes only support simple binary comparison and do not support the collation option.

To create a 2d index on a collection that has a non-simple collation, you must explicitly specify {collation: {locale: "simple"} } when creating the index.

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Query a 2dsphere Index