center.txt

=======
$center
=======

.. default-domain:: mongodb

.. contents:: On this page
   :local:
   :backlinks: none
   :depth: 1
   :class: singlecol

Definition
----------

.. query:: $center

   The :query:`$center` operator specifies a circle for a
   :query:`$geoWithin` query. The query returns legacy coordinate pairs
   that are within the bounds of the circle. The operator does *not*
   return GeoJSON objects.

   To use the :query:`$center` operator, specify an array that
   contains:

   - The grid coordinates of the circle's center point, and

   - The circle's radius, as measured in the units used by the
     coordinate system.

   .. code-block:: javascript

      {
         <location field>: {
            $geoWithin: { $center: [ [ <x>, <y> ] , <radius> ] }
         }
      }

   .. important::
      If you use longitude and latitude, specify **longitude first**.

Behavior
--------

The query calculates distances using flat (planar) geometry.

.. |operator| replace:: :query:`$center`
.. include:: /includes/note-geospatial-index-must-exist.rst

Only the :doc:`2d </core/2d>` geospatial index supports
:query:`$center`.

Example
-------

The following example query returns all documents that have coordinates
that exist within the circle centered on ``[ -74, 40.74 ]`` and with a
radius of ``10``:

.. code-block:: javascript

   db.places.find(
      { loc: { $geoWithin: { $center: [ [-74, 40.74], 10 ] } } }
   )