How to setup geocoding for "Nearby Groups"

Almost all of our groups are based on locations such as countries or parts of countries (states in the USA). So I would like to use the "Nearby Groups" button to display such groups. I don't see any settings in ES -> Dashboard -> Groups -> Groups or the Settings area. I assume some geocoding will be involved.

But I'm not having any luck finding documentation or forums posts explaining how to set up this feature.

Could you please point me either to the documentation or explain?

Thanks. -- Rik