Description
In the docs for the $geoNear aggregation operator
http://docs.mongodb.org/manual/reference/operator/aggregation/geoNear/
it's stated:
- The collection must have a geospatial index.
- The $geoNear requires that a collection have at most only one 2d index and/or only one 2dsphere index.
However, it would be useful to then explicitly state that the location field does not need to be specified to the operator, since the 2d/2dsphere field from the geospatial index is what will (implicitly) be used.