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Isochrone: A polygon that demonstrates the travel distance by time from a given location based on the existing surrounding infrastructure or environment. Given their dependence on (most often) a transportation infrastructure, these polygons scatter in an elongated pattern along each major line.
Geofence: is a virtual boundary that adheres to a given location based on customized criteria. If you think of your home, you would consider your entire land parcel as part of your property. The land parcel boundary polygon would be the geofence. (Now if I could just figure out a way to get the neighborhood cat to adhere to that as a restricted boundary!)
For the purposes of marketing, an isochrone would be more applicable for outreach to customers if they are within a specific driving distance or happen to cross into the isochrone (or at least their mobile device does). This is outreach marketing or casting a net to potential customers close enough to be enticed into a store.
A geofence, on the other hand, is used to identify when customers are arriving at (or currently at) a given location. The classic example is a major brand store in a mall will build a geofence around the entire mall property and will send advertisements to those within the boundary to entice customers that are already at the mall to visit their store. Another example is when one major home improvement store builds a geofence around their competition's locations and sends them advertisements to entice them away from that location and into the closest store. Geofence marketing is targeted marketing for customers that are already within a confined area.
In short, isochrones are for marketing to people nearby or that come close to a location, while geofencing is for marketing to those already at or arriving at a location.
How do you use isochrones and geofences differently? Do you prefer one over the other?