Dirsch and Haunert – METROCHRONES 2023

Description

The paper introduces Metrochrones: an algorithm to generate schematic isochrones for octilinear transit maps, producing region boundaries that include all reachable stations and exclude unreachable ones. Unlike road-based isochrones, reachability is station-centered, allowing flexible separation points; a pre-computed octilinear grid yields a solution space. The method planarizes the transit graph, identifies gates and reachability-splitting faces, extracts grid subgraphs per face, joins them into a routing graph, and finds a minimum-cost closed path (isoline) via shortest-path routing on a pseudo-dual graph. Optimization uses weighted cost functions to enforce design criteria: minimize bends, avoid acute crossings, keep distance from existing lines, and increase compactness; two bend penalties (uniform and angle-weighted) are compared. Evaluation on Cologne and Paris networks shows fast runtimes (seconds), good trade-offs among criteria, and near–designer quality with parameter tuning. Limitations include parameter sensitivity and independent zone generation (possible overlaps); code and examples are available open-source.