The lifetime of a sputtering target is related to the magnetic field distribution near the target surface, which is related to the magnets' arrangement underneath the target. Therefore, a key design issue is the placement of the magnets to ensure an optimum target lifetime. Even in maintenance procedures it may be necessary to know the magnetic field distribution near the target. This work presents a technique which can be used to map the magnetic field over large targets. The system uses a custom made acquisition board, a modified plotter, and a Hall sensor to measure the two-dimensional magnetic field configuration at different heights near the target. It has been tested with success to measure a 62 mmX226 mm target area in the three coordinates.