Supplementing Electronic Map Data from User Behavior

There is provided a method for identifying possible errors/inconsistencies within an electronic map representation of a network of navigable elements within a geographic area, the method comprising: obtaining at a server positional data relating to the movement over time of a plurality of devices travelling around the navigable network; processing the obtained positional data at the server with reference to the electronic map representing the navigable network in order to identify potential inconsistencies in the map in the form of one or more locations within the navigable network where an observed behaviour of devices travelling around the navigable network as indicated by the obtained positional data is not consistent with a behaviour that would be expected based on the electronic map. This information may then be relayed to navigation devices for supplementing the electronic map when generating navigation instructions.