A method is described for creating observation data, in particular by at least one vehicle, traveled road segments being ascertained by the vehicle, lanes of the road segments traveled by the vehicle being ascertained by the vehicle, and the ascertained road segments together with the ascertained traveled lanes being transmitted as observation data from the vehicle to an external server unit. A method for ascertaining a number of traffic lanes, to a system, to an external server unit, and to a control unit are also described.