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Query a 2d Index¶
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The following sections describe queries supported by the 2d index.
Points within a Shape Defined on a Flat Surface¶
To select all legacy coordinate pairs found within a given shape on a flat surface, use the $geoWithin operator along with a shape operator. Use the following syntax:
db.<collection>.find( { <location field> :
{ $geoWithin :
{ $box|$polygon|$center : <coordinates>
} } } )
The following queries for documents within a rectangle defined by [ 0 , 0 ] at the bottom left corner and by [ 100 , 100 ] at the top right corner.
db.places.find( { loc :
{ $geoWithin :
{ $box : [ [ 0 , 0 ] ,
[ 100 , 100 ] ]
} } } )
The following queries for documents that are within the circle centered on [ -74 , 40.74 ] and with a radius of 10:
db.places.find( { loc: { $geoWithin :
{ $center : [ [-74, 40.74 ] , 10 ]
} } } )
For syntax and examples for each shape, see the following:
Points within a Circle Defined on a Sphere¶
MongoDB supports rudimentary spherical queries on flat 2d indexes for legacy reasons. In general, spherical calculations should use a 2dsphere index, as described in 2dsphere Indexes.
To query for legacy coordinate pairs in a “spherical cap” on a sphere, use $geoWithin with the $centerSphere operator. Specify an array that contains:
- The grid coordinates of the circle’s center point
- The circle’s radius measured in radians. To calculate radians, see Calculate Distance Using Spherical Geometry.
Use the following syntax:
db.<collection>.find( { <location field> :
{ $geoWithin :
{ $centerSphere : [ [ <x>, <y> ] , <radius> ] }
} } )
The following example query returns all documents within a 10-mile radius of longitude 88 W and latitude 30 N. The example converts distance to radians by dividing distance by the approximate equatorial radius of the earth, 3963.2 miles:
db.<collection>.find( { loc : { $geoWithin :
{ $centerSphere :
[ [ 88 , 30 ] , 10 / 3963.2 ]
} } } )
Proximity to a Point on a Flat Surface¶
Proximity queries return the 100 legacy coordinate pairs closest to the defined point and sort the results by distance. Use either the $near operator or geoNear command. Both require a 2d index.
The $near operator uses the following syntax:
db.<collection>.find( { <location field> :
{ $near : [ <x> , <y> ]
} } )
For examples, see $near.
The geoNear command uses the following syntax:
db.runCommand( { geoNear: <collection>, near: [ <x> , <y> ] } )
The geoNear command offers more options and returns more information than does the $near operator. To run the command, see geoNear.
Exact Matches on a Flat Surface¶
Changed in version 2.6: Previously, 2d indexes would support exact-match queries for coordinate pairs.
You cannot use a 2d index to return an exact match for a coordinate pair. Use a scalar, ascending or descending, index on a field that stores coordinates to return exact matches.
In the following example, the find() operation will return an exact match on a location if you have a { 'loc': 1} index:
db.<collection>.find( { loc: [ <x> , <y> ] } )
This query will return any documents with the value of [ <x> , <y> ].
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