Each sensor can determine varying pressure values. In other words, the sensors can determine how hard the user is pushing down on the glass. And when the user presses down on one sensor, the other sensors go off as though they were touched with less force than the sensor that actually received the input. That helps the sensors determine the point of origin. The system can even know when a swipe or gesture started off-screen. That is important because currently, a swipe left or right from the edge of the screen might not register
Deploying the sensors on off-screen buttons can allow more of the the screen to be used to display things. This patent differs from one revealed back in November that dealt with force sensors being placed under the glass of a touchscreen. That patent covered a method for determining how hard the screen was being touched, while this patent covers a system for determining where that touch is coming from.
Apple applies for a new patent dealing with pressure-sensitive input on a touchscreen
1. Method in patent application will allow input gestures to start or end off-screen
2. Force sensor is placed under the glass
source: USPTO via AppleInsider