See also:
Expr::maxDistance()
See also:
http://docs.mongodb.org/manual/reference/command/geoNear/
See also:
http://docs.mongodb.org/manual/reference/operator/maxDistance/
See also:
http://docs.mongodb.org/manual/reference/operator/near/
See also:
http://docs.mongodb.org/manual/reference/operator/nearSphere/