A method for determining a spatially resolved extent of error for position finding with a global navigation satellite system for a target area of interest using field data from a plurality of field apparatuses, particularly motor vehicles, each having a receiver for the global navigation satellite system and which are at least intermittently situated in the target area, comprising the following steps: ascertainment by the field apparatuses of at least one field data record comprising a current GNSS position in the target area and an error value associated with said position, transmission of the field data records to a central computation device, updating of an error map containing the extents of error for various positions and/or subareas of the target area by statistical evaluation of the field data records in the central computation device.