Geolocation queries

Geolocation is in-built into MongoDB, and is one of its distinguishing features. We have seen examples of 2d or 2dsphere index in earlier chapters, and also seen how we can use the near criterion. Using $geoNear, that is, the geo_near method we can get geospatial criteria easily.

One of the common problems in geospatial search is that the queries use radians and not distance units (kilometers, or miles). MongoDB provides a distanceMultiplier operator that we can use to ensure consistency.

So, this query will give results with the distance in miles:

Author.geo_near([ 50, 13 ]).distance_multiplier(3959)

Tip

The earth has a radius of approximately 3,959 miles or 6,371 km.

Suppose, we find all authors within a 10 miles radius of [34.052923, -84.44399]. First and foremost, when using only latitude and longitude, using a 2dsphere index is recommended. So, let's modify the Author model.

class Address
  include Mongoid::Document
  ...

 field :location, type: Array  # the location co...