The thing about MongoDB and JSON that makes it so nice to use is the fact that JSON stands for JavaScript Object Notation. JavaScript is a programming language which is easy to understand and can achieve almost anything.
So JSON was made for JavaScript and can be very easily incorporated into a JavaScript program. Geographical data are used by libraries to make working with this particular type of JSON easier.
Leaflet
LeafletJS is a JavaScript library used to display map data. Sometimes it is necessary to make an application which displays a map.
Perhaps one needs to design an application which tracks employees on a day-to-day basis. LeafletJS allows one to easily integrate with a MongoDB when it comes to geographical data.
Leaflet already knows the difficulties of displaying a map and takes care of all the issues for you. Your only concern is the data with which you are working.
MongoDB Spatial Tutorial 