When you embed a GPS location into a pass template (or a pass), and assign a message to this GPS location, the pass holder will see this message when in proximity.
One frequently asked question is how close does the pass holder need to be to the GPS coordinates to see the message.
Firstly, it's important to note that it's NOT an exact distance. Both Apple's and Google's algorithm considers GPS, Wifi, Bluetooth, movement, dwell time and other factors. When the user is determined to be physically present, a geofenced notification is triggered.
Depending on the type of pass you've selected, the relevance information is interpreted in slightly different ways. When the location is interpreted with a small radius, the current location must be on the order of a hundred meters or closer; with a large radius, on the order of a thousand meters or closer. In both cases, the exact relevance radius is an implementation detail and may change.
Boarding passes are interpreted with a large radius (thousand of meters or closer). All other pass types are intepreted with a small radius (hundreds of meters or closer).