geofence
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A geofence is a virtual geographic boundary that either triggers or limits actions, information, or granularity thereof when crossing it, like 
Aaron Parecki’s pulsing blue dot feature.
IndieWeb Examples
Aaron Parecki
Aaron Parecki’s site creates a dynamic geofence around his latest checkin, to show a pulsing blue dot if he is still at or nearby, and removes the blue dot from the checkin post when he leaves the geofence, since 2017-05-19.
- Post about it: 2017-05-19: I'm Still Here!
David Shanske
The geofences, called Zones in the plugin, create a radius around a point where the description will be displayed as the name of the zone and the coordinates and map will be hidden. This can be overridden in the post UI manually and will not be retroactively applied to older posts.
Brainstorming
The most common uses for geofencing for a website can allow changes to the site when a geofence is entered/exited. For example, displaying that someone is currently in a place. Alternatively, it can disable sharing that information when someone is in a specifically private place that they do not wish to share. The most common place that fits this use case is one's home.
Other possibilities that could be implemented would be automatically posting to your site when you enter a certain location/locations...an automatic rather than manual posting of a checkin at a regular hangout.