A survey of direction-preserving layout strategies

In this paper we analyze different layout algorithms that preserve relative directions in geo-referenced networks. This is an important criterion for many sensor networks such as the electric grid and other supply networks, because it enables the user to match the geographic setting with the drawing on the screen. Even today, the layout of these networks are often created manually. This is due to the requirement that these layouts must respect geographic references but should still be easy to read and understand. The range of available automatic algorithms spans from general graph layouts over schematic maps to semi-realistic drawings. At first sight, schematics seem to be a promising compromise between geographic correctness and readability. The former property exploits the mental map of the user while the latter makes it easier for the user to learn about the network structure. We investigate different algorithms for such maps together with different visualization techniques. In particular, the group of octi-linear layouts is prominent in handcrafted subway maps. These algorithms have been used extensively to generate drawings for subway maps. Also known as Metro Map layouts, only horizontal, vertical and diagonal directions are allowed. This increases flexibility and makes the resulting layout look similar to the well-known subway maps of large cities. The key difference to general graph layout algorithms is that geographic relations are respected in terms of relative directions. However, it is not clear, whether this metaphor can be transferred from metro maps to other domains. We discuss applicability of these different approaches for geo-based networks in general with the electric grid as a use-case scenario.