There is provided a method for generating traffic data indicative of a traffic volume and/or traffic density within a navigable network in an area covered by an electronic map, the electronic map comprising a plurality of segments representing navigable elements of the navigable network. The method generally comprises obtaining positional data relating to the movement of a plurality of devices along the navigable elements represented by the segments of the electronic map; determining, using (at least) positional data relating to one or more congested segments within a region of the navigable network, an estimate of one or more average penetration rates for the region; determining a sample volume for a non-congested segment within the region based on the obtained positional data; and estimating, using the determined sample volume and a selected one of the average penetration rates for the region, a traffic volume and/or traffic density for the non-congested segment. Also provided are systems for performing the method. Accordingly, traffic volume and/or traffic densities can be estimated from probe data.