The Geofence Function is used to check whether a certain Latitude and Longitude position is inside or outside a given geographic area. For example, to check if a moving asset is within a geographic area. This function supports Polygonal Geofences.
A polygonal geofence is created using a set of Latitude and Longitude values which, as the name suggests, represents a polygon.
You can use an online tool to create a static geofence file - which is primarily a CSV file of Latitude and Longitude pairs - an example can be found here. Or you can supply the data dynamically for a moving geofence.