Designing and annotating metro maps with loop lines

Schematic metro maps provide an effective means of simplifying the geographical configuration of public rapid transportation systems. Nonetheless, travelers still find it difficult to identify routes of a specific topology on the maps because it is usually hidden behind the conventional octilinear layout of the entire map. In this paper, we present an approach to designing schematic maps with loop lines, which are drawn as circles together with annotation labels for guiding different traveling purposes. Our idea here is to formulate the aesthetic criteria as mathematical constraints in the mixed-integer programming model, which allows us to either align stations on the loop line at a grid if they are interchange stations or noninterchange stations on a circle otherwise. We then distribute the annotation labels associated with stations on the loop line evenly to the four side boundary of the map domain in order to make full use of the annotation space, while maximally avoiding intersections between leader lines and the metro network by employing a flow network algorithm. Finally, we present several experimental results generated by our prototype system to demonstrate the feasibility of the proposed approach.