Pressure sensor matrices are multi-touch pressure sensors, often found in DIY and e-textile sensor designs. Some examples:
They consist of electrodes arranged in rows and columns, separated by a piezo-resistive material. Using a microcontroller one samples the sensor by looping through each row & column combination and sampling the resistance at that point.
The data can then be used in various ways. The image below shows a computer-vision based approach. In our work we suggest using sup-pixel peak-detection algorithms.