$geoNear (aggregation)¶

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Definition
Behavior
Examples

Definition¶

$geoNear¶

Outputs documents in order of nearest to farthest from a specified point.

The $geoNear stage has the following prototype form:

{ $geoNear: { <geoNear options> } }

The $geoNear operator accepts a document that contains the following $geoNear options. Specify all distances in the same units as those of the processed documents’ coordinate system:

Field	Type	Description
`spherical`	boolean	Determines how MongoDB calculates the distance between two points: When `true`, MongoDB uses `$nearSphere` semantics and calculates distances using spherical geometry. When `false`, MongoDB uses `$near` semantics: spherical geometry for 2dsphere indexes and planar geometry for 2d indexes. Default: false.
`limit`	number	Optional. The maximum number of documents to return. The default value is `100`. See also the `num` option.
`num`	number	Optional. The `num` option provides the same function as the `limit` option. Both define the maximum number of documents to return. If both options are included, the `num` value overrides the `limit` value.
`maxDistance`	number	Optional. The maximum distance from the center point that the documents can be. MongoDB limits the results to those documents that fall within the specified distance from the center point. Specify the distance in meters if the specified point is GeoJSON and in radians if the specified point is legacy coordinate pairs.
`query`	document	Optional. Limits the results to the documents that match the query. The query syntax is the usual MongoDB read operation query syntax. You cannot specify a `$near` predicate in the `query` field of the `$geoNear` stage.
`distanceMultiplier`	number	Optional. The factor to multiply all distances returned by the query. For example, use the `distanceMultiplier` to convert radians, as returned by a spherical query, to kilometers by multiplying by the radius of the Earth.
`uniqueDocs`	boolean	Optional. If this value is `true`, the query returns a matching document once, even if more than one of the document’s location fields match the query. Deprecated since version 2.6: Geospatial queries no longer return duplicate results. The `$uniqueDocs` operator has no impact on results.
`near`	GeoJSON point or legacy coordinate pair	The point for which to find the closest documents. If using a 2dsphere index, you can specify the point as either a GeoJSON point or legacy coordinate pair. If using a 2d index, specify the point as a legacy coordinate pair.
`distanceField`	string	The output field that contains the calculated distance. To specify a field within an embedded document, use dot notation.
`includeLocs`	string	Optional. This specifies the output field that identifies the location used to calculate the distance. This option is useful when a location field contains multiple locations. To specify a field within an embedded document, use dot notation.
`minDistance`	number	Optional. The minimum distance from the center point that the documents can be. MongoDB limits the results to those documents that fall outside the specified distance from the center point. Specify the distance in meters for GeoJSON data and in radians for legacy coordinate pairs. New in version 3.2.
`key`	string	Optional. Specify the geospatial indexed field to use when calculating the distance. If your collection has multiple `2d` and/or multiple `2dsphere` indexes, you must use the `key` option to specify the indexed field path to use. Specify Which Geospatial Index to Use provides a full example. If there is more than one `2d` index or more than one `2dsphere` index and you do not specify a `key`, MongoDB will return an error. 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. New in version 4.0.

Behavior¶

When using $geoNear, consider that:

You can only use $geoNear as the first stage of a pipeline.
You must include the distanceField option. The distanceField option specifies the field that will contain the calculated distance.
$geoNear requires a geospatial index.

If you have more than one geospatial index on the collection, use the keys parameter to specify which field to use in the calculation. If you have only one geospatial index, $geoNear implicitly uses the indexed field for the calculation.

You cannot specify a $near predicate in the query field of the $geoNear stage.
Views do not support geoNear operations (i.e. $geoNear pipeline stage and the deprecated geoNear command).

Generally, the options for $geoNear are similar to the deprecated geoNear command with the following exceptions:

distanceField is a mandatory field for the $geoNear pipeline operator; the option does not exist in the geoNear command.
includeLocs accepts a string in the $geoNear pipeline operator and a boolean in the geoNear command.

Examples¶

Create a collection places with the following documents:

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db.places.insertMany( [
   {
      name: "Central Park",
      location: { type: "Point", coordinates: [ -73.97, 40.77 ] },
      category: "Parks"
   },
   {
      name: "Sara D. Roosevelt Park",
      location: { type: "Point", coordinates: [ -73.9928, 40.7193 ] },
      category: "Parks"
   },
   {
      name: "Polo Grounds",
      location: { type: "Point", coordinates: [ -73.9375, 40.8303 ] },
      category: "Stadiums"
   }
] )

The following operation creates a 2dsphere index on the location field:

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db.places.createIndex( { location: "2dsphere" } )

Maximum Distance¶

The places collection above has a 2dsphere index. The following aggregation uses $geoNear to find documents with a location at most 2 meters from the center [ -73.99279 , 40.719296 ] and category equal to Parks.

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db.places.aggregate([
   {
     $geoNear: {
        near: { type: "Point", coordinates: [ -73.99279 , 40.719296 ] },
        distanceField: "dist.calculated",
        maxDistance: 2,
        query: { type: "public" },
        includeLocs: "dist.location",
        num: 5,
        spherical: true
     }
   }
])

The aggregation returns the following:

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{
   "_id" : 8,
   "name" : "Sara D. Roosevelt Park",
   "type" : "public",
   "location" : {
      "type" : "Point",
      "coordinates" : [ -73.9928, 40.7193 ]
   },
   "dist" : {
      "calculated" : 0.9539931676365992,
      "location" : {
         "type" : "Point",
         "coordinates" : [ -73.9928, 40.7193 ]
      }
   }
}

The matching document contains two new fields:

dist.calculated field that contains the calculated distance, and
dist.location field that contains the location used in the calculation.

Minimum Distance¶

New in version 3.2.

The following example uses the option minDistance to specify the minimum distance from the center point that the documents can be. MongoDB limits the results to those documents that fall outside the specified distance from the center point.

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db.places.aggregate([
   {
     $geoNear: {
        near: { type: "Point", coordinates: [ -73.99279 , 40.719296 ] },
        distanceField: "dist.calculated",
        minDistance: 2,
        query: { type: "public" },
        includeLocs: "dist.location",
        num: 5,
        spherical: true
     }
   }
])

Specify Which Geospatial Index to Use¶

New in version 4.0.

Consider a places collection that has a 2dsphere index on the location field and a 2d index on the legacy field.

A document in the places collection resembles the following:

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{
   "_id" : 3,
   "name" : "Polo Grounds",
   "location": {
      "type" : "Point",
      "coordinates" : [ -73.9375, 40.8303 ]
   },
   "legacy" : [ -73.9375, 40.8303 ],
   "category" : "Stadiums"
}

The following example uses the keys option to specify that the aggregation should use the location field values for the $geoNear operation rather than the legacy field values.

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db.places.aggregate([
   {
     $geoNear: {
        near: { type: "Point", coordinates: [ -73.98142 , 40.71782 ] },
        key: "location",
        distanceField: "dist.calculated",
        query: { "category": "Parks" }
     }
   }
])

The aggregation returns the following:

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{
   "_id" : 2,
   "name" : "Sara D. Roosevelt Park",
   "location" : {
      "type" : "Point",
      "coordinates" : [
         -73.9928,
         40.7193
      ]
   },
   "category" : "Parks",
   "dist" : {
      "calculated" : 974.175764916902
   }
}
{
   "_id" : 1,
   "name" : "Central Park",
   "location" : {
      "type" : "Point",
      "coordinates" : [
         -73.97,
         40.77
      ]
   },
   "legacy" : [
      -73.97,
      40.77
   ],
   "category" : "Parks",
   "dist" : {
      "calculated" : 5887.92792958097
   }
}

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