$geoWithin

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Definition

Behavior
Examples

Definition

$geoWithin

Selects documents with geospatial data that exists entirely within a specified shape.

The specified shape can be either a GeoJSON Polygon (either single-ringed or multi-ringed), a GeoJSON MultiPolygon, or a shape defined by legacy coordinate pairs. The $geoWithin operator uses the $geometry operator to specify the GeoJSON object.

To specify a GeoJSON polygons or multipolygons using the default coordinate reference system (CRS), use the following syntax:

{
   <location field>: {
      $geoWithin: {
         $geometry: {
            type: <"Polygon" or "MultiPolygon"> ,
            coordinates: [ <coordinates> ]
         }
      }
   }
}

For $geoWithin queries that specify GeoJSON geometries with areas greater than a single hemisphere, the use of the default CRS results in queries for the complementary geometries.

To specify a single-ringed GeoJSON polygon with a custom MongoDB CRS, use the following prototype that specifies the custom MongoDB CRS in the $geometry expression:

{
   <location field>: {
      $geoWithin: {
         $geometry: {
           type: "Polygon" ,
           coordinates: [ <coordinates> ],
           crs: {
              type: "name",
              properties: { name: "urn:x-mongodb:crs:strictwinding:EPSG:4326" }
           }
         }
      }
   }
}

The custom MongoDB CRS uses a counter-clockwise winding order and allows $geoWithin to support queries with a single-ringed GeoJSON polygon whose area is greater than or equal to a single hemisphere. If the specified polygon is smaller than a single hemisphere, the behavior of $geoWithin with the MongoDB CRS is the same as with the default CRS. See also "Big" Polygons.

If querying for inclusion in a shape defined by legacy coordinate pairs on a plane, use the following syntax:

{
   <location field>: {
      $geoWithin: { <shape operator>: <coordinates> }
   }
}

The available shape operators are:

$box,
$polygon,
$center (defines a circle), and
$centerSphere (defines a circle on a sphere).

Important

If you use longitude and latitude, specify coordinates in order of longitude, latitude.

Behavior

Geospatial Indexes

$geoWithin does not require a geospatial index. However, a geospatial index will improve query performance. Both 2dsphere and 2d geospatial indexes support $geoWithin.

Unsorted Results

The $geoWithin operator does not return sorted results. As such, MongoDB can return $geoWithin queries more quickly than geospatial $near or $nearSphere queries, which sort results.

Degenerate Geometry

$geoWithin does not guarantee that it will consider a piece of geometry to contain its component geometry, or another polygon sharing its component geometry.

"Big" Polygons

For $geoWithin, if you specify a single-ringed polygon that has an area greater than a single hemisphere, include the custom MongoDB coordinate reference system in the $geometry expression; otherwise, $geoWithin queries for the complementary geometry. For all other GeoJSON polygons with areas greater than a hemisphere, $geoWithin queries for the complementary geometry.

Examples

Within a Polygon

The following example selects all loc data that exist entirely within a GeoJSON Polygon. The area of the polygon is less than the area of a single hemisphere:

db.places.find(
   {
     loc: {
       $geoWithin: {
          $geometry: {
             type : "Polygon" ,
             coordinates: [ [ [ 0, 0 ], [ 3, 6 ], [ 6, 1 ], [ 0, 0 ] ] ]
          }
       }
     }
   }
)

For single-ringed polygons with areas greater than a single hemisphere, see Within a "Big" Polygon.

Within a "Big" Polygon

To query with a single-ringed GeoJSON polygon whose area is greater than a single hemisphere, the $geometry expression must specify the custom MongoDB coordinate reference system. For example:

db.places.find(
   {
     loc: {
       $geoWithin: {
          $geometry: {
             type : "Polygon" ,
             coordinates: [
               [
                 [ -100, 60 ], [ -100, 0 ], [ -100, -60 ], [ 100, -60 ], [ 100, 60 ], [ -100, 60 ]
               ]
             ],
             crs: {
                type: "name",
                properties: { name: "urn:x-mongodb:crs:strictwinding:EPSG:4326" }
             }
          }
       }
     }
   }
)

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$geoIntersects

$near