# Calculate Distance Using Spherical Geometry¶

Note

While basic queries using spherical distance are supported by the `2d` index, consider moving to a `2dsphere` index if your data is primarily longitude and latitude.

The `2d` index supports queries that calculate distances on a Euclidean plane (flat surface). The index also supports the following query operators and command that calculate distances using spherical geometry:

Important

These three queries use radians for distance. Other query types do not.

For spherical query operators to function properly, you must convert distances to radians, and convert from radians to the distances units used by your application.

To convert:

• distance to radians: divide the distance by the radius of the sphere (e.g. the Earth) in the same units as the distance measurement.
• radians to distance: multiply the radian measure by the radius of the sphere (e.g. the Earth) in the units system that you want to convert the distance to.

The equatorial radius of the Earth is approximately `3,963.2` miles or `6,378.1` kilometers.

The following query would return documents from the `places` collection within the circle described by the center `[ -74, 40.74 ]` with a radius of `100` miles:

You may also use the `distanceMultiplier` option to the `geoNear` to convert radians in the `mongod` process, rather than in your application code. See distance multiplier.

The following spherical query, returns all documents in the collection `places` within `100` miles from the point ```[ -74, 40.74 ]```.

The output of the above command would be:

Warning

Spherical queries that wrap around the poles or at the transition from `-180` to `180` longitude raise an error.

Note

While the default Earth-like bounds for geospatial indexes are between `-180` inclusive, and `180`, valid values for latitude are between `-90` and `90`.

## Distance Multiplier¶

The `distanceMultiplier` option of the `geoNear` command returns distances only after multiplying the results by an assigned value. This allows MongoDB to return converted values, and removes the requirement to convert units in application logic.

Using `distanceMultiplier` in spherical queries provides results from the `geoNear` command that do not need radian-to-distance conversion. The following example uses `distanceMultiplier` in the `geoNear` command with a spherical example:

The output of the above operation would resemble the following: