Let's say I have the maps addon all set, and each post has an address. If a user gives me their address, is there a mechanism for showing all the addresses with X distance of that address?
Unfortunately, the Google map field of Meta Box doesn't support that feature. You will need to create some custom code to do that or use a third-party plugin that supports the distance feature.
Please follow the documentation https://developers.google.com/maps/documentation/javascript/distancematrix
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