1. A method for determining a position of a motor vehicle, comprising: determining on a digital road map the position of the motor vehicle on a roadway by way of satellite-based positioning (GPS), wherein the roadway has at least one road sign located at a known relative distance from a reference point having a known geographic position and the roadway is an interstate highway, determining on the digital map a virtual route to be traveled by the motor vehicle to the reference point along the roadway, optically capturing with a camera located in or on the vehicle the at least one road sign having distance information showing the relative distance, wherein the road sign is captured, while driving, at a first time instance and the position of the motor vehicle is determined at a second time instance, when the road sign leaves the capture region at the second time instance, evaluating the at least one road sign using optical character recognition to determine the relative distance to the reference point, matching the determined relative distance to the reference point with map data stored on the digital road map by taking into account the position of the motor vehicle determined by GPS and the travel along the virtual route, and positioning the motor vehicle on the digital road map when the distance from the position of the motor vehicle to the reference point on the digital road map is identical to the determined relative distance.