National-Scale Multimodal Accessibility Fields from Open Geospatial Data
MAPPER is an open-data, C++/OpenMP-powered pipeline that builds walk, bike, car, and public transport travel-time graphs from OpenStreetMap and GTFS data to generate continuous accessibility fields using network kernel density estimation. A full-country deployment across Germany generated an H3-indexed grid dataset containing nearly 40 million cells and 972 mode-layer fields spanning nine intermodal and network modes. Validation against an empirical mobility panel confirmed low mean bias for road and active travel, while public transit outputs serve as schedule-based supply estimates.
Why it matters — Researchers can now run continent- or national-scale multimodal accessibility models combining custom opportunity layers on standard commodity hardware without specialized computing infrastructure.
Caveat: Public transit travel times rely on schedule supply models rather than observed trips, making them sensitive to default transfer and waiting time parameters.