An electronic route guidance system employing roadside processors will benefit from the provision of a compact method of storing directional information, especially when a large network is involved. This may be particularly relevant where roadside units are periodically downloaded from a central installation. A form of quadtree, the partition tree, offers very efficient data storage together with the ability to support alternative directions for different vehicle types, time periods and other parameters with the minimum use of additional memory. In a network of 40000 nodes, the largest considered, the estimated average size of partition tree is 686 bytes, and the maximum size around 2k bytes. In a main-road-only network, containing 10000 nodes, these figures are approximately halved.