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Network data sources
Every accessibility study starts with a decision about network data. The choice constrains which modes can be modelled, which areas can be covered, and how much cleaning work follows.
| Source | Coverage | Modes | Licence | Main limitation |
|---|---|---|---|---|
| OSM | Global | Car, bicycle, pedestrian, (rail) | ODbL | Variable completeness and tagging quality |
| NWB | Netherlands | Car, cycle/footpaths as separate file | Open | National only; cross-border routes not represented |
| GTFS | Per transit operator/region | Public transport | Varies | Timetables only; no infrastructure geometry |
| Commercial (TomTom, HERE) | Global | Car | Proprietary | Cost; but includes speed profiles by time of day |
Sources are routinely combined: OSM geometry for cycling and walking, a commercial source for car speed profiles reflecting congestion, and GTFS for transit. The Dutch national network model does exactly this — see the network model documentation.
- Modes. Does it contain cycle and foot paths, or only roads a car can use? A car-only file makes pedestrian accessibility impossible, not merely approximate.
- Extent and edges. Does it cover the area around your study area? Many fastest routes within the Netherlands run through Belgium or Germany, and a national-only file will route them the long way. See Zoning and spatial units on edge effects.
- Directionality and restrictions. One-way flags, turn restrictions, access tags (private roads, bus lanes, pedestrian zones).
- Connectivity. Whether links that cross actually share a node — see Building a routable network. Bridges and tunnels must not connect.
- Attributes for speed. Road classification, speed limits, surface — the inputs to Travel speeds per mode.
- Update frequency and versioning. A reproducible study needs a dated snapshot, not "current".
- Building a routable network — turning a data file into a graph
- Travel speeds per mode — assigning impedance to links
- Euclidean versus network distance — what you lose without a network
Concepts
Networks
- Network data sources
- OSM
- NWB
- GTFS
- Building a routable network
- Network optimisation algorithm
- Travel speeds per mode
Origins & destinations
Computation
- Shortest path and the Dijkstra algorithm
- Origin Destination matrix (trip table)
- Isochrones and catchment areas
- Public transport routing
Indicators
Applications
Network models
Reference