A multi-electrode capacitive sensor is introduced to measure a spatial distribution of impedances to ground. The sensor can be used to identify the location of the highest impedance on the seating surface and can be a two-electrode sensor with a first electrode covering a central zone of a seat cushion and a second electrode with two galvanically connected electrode members, wherein each electrode member covers one side region of the seat cushion such that the first antenna electrode is arranged between the two electrode members of the second antenna electrode, or a two-electrode sensor with a left and right design. By measuring the difference of the impedance to ground between the two zones the system can get a simplified picture of the impedance distribution on the seating surface. This information can be used to distinguish between grounded structures such as (ISOFIX) child restraint systems and human occupants.