NAVIGATION DEVICES

A method of creating map data, including search acceleration data arranged to increase the speed at which a route can be planned across an electronic map, which comprises a plurality of navigable segments, representing segments of a navigable route in the area covered by the map, wherein the method comprises: a) processing the navigable segments in order to generate the search acceleration data for at least some of, and generally each of, the navigable segments of the electronic map indicating whether that navigable segment is part of a minimum cost route; and b) processing the generated search acceleration data in order to compress that data wherein the compression includes computing the correlation of pairs of bits in the search acceleration data and coalescing correlated bits.