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NetworkModel_World is a global road network model. It builds a routable car network for the entire world from OpenStreetMap data, connects that network to global population grids and settlement layers, and then derives a set of accessibility products from it: settlement hierarchies, catchment areas of central places, travel times and travel distances to settlements of a given size, functional rural areas, and a proxy for the distances people travel.
The model was built by Object Vision in the GeoDMS software. It is fully based on open data. Everything is computed globally and consistently, so that results for one country can be compared with results for any other country, including flows and catchments that cross national borders.
The products of this model are used in several ways. They are policy relevant in their own right, for example the rural accessibility and functional rural area work carried out for the OECD. They also serve as prepared input for other models. In particular, the global network and its derived accessibility grids feed into the CRISP model, where they act as locational suitability drivers for the downscaling of built-up land and population. See Use in CRISP for that connection.
The model works per continent for network construction and per country for the analyses. That split matters: a routable global network cannot be held in memory in one piece, while most result products are requested and delivered per country.
Source data
Three global datasets carry the model. OpenStreetMap extracts from Geofabrik, delivered as .pbf files per world region, provide the road geometry, road classes and speed tags. The GHSL population grid provides population at 1 km resolution in World Mollweide. The GHSL settlement model layer (SMOD) provides settlement polygons in four classes, from villages to cities. Country and continent boundaries, separated country parts, OECD functional urban areas and a set of functional areas complete the input side. See Geography for how the spatial units are defined.
Network construction
OSM lines are filtered down to the part of the network a car can use, including car ferries. Every line is cut into segments, each segment gets a speed either from its maxspeed tag or from a lookup table by road type, and the resulting graph is checked for connectivity so that isolated fragments are dropped. Population grid cells and settlement centroids are then connected to the network as origins and destinations. Finally the network is compressed: nodes that are not junctions and not connection points are removed, and the chains between junctions are collapsed into single links with aggregated impedance. This step is repeated ten times and typically removes a large share of the links without changing any travel time.
Settlement hierarchies
For every settlement the model determines, for each of 25 travel time thresholds from 0 to 120 minutes in steps of 5 minutes, whether it is the most populous settlement reachable within that threshold. The highest threshold at which a settlement still dominates its surroundings is its rank. This yields a continuous hierarchy from local centre to national centre, computed from the network rather than from administrative status.
Catchments and Functional rural areas
Given a set of centres, every populated grid cell is assigned to the centre it can reach fastest over the network. Grid cells that cannot be connected to the network are handled separately so that islands and exclaves still get an assignment. The resulting cell assignments are dissolved into catchment polygons and cleaned in ten iterations, which removes slivers and reattaches non contiguous fragments to a sensible neighbour. Catchments are then aggregated further into functional rural areas under a target population size and travel time constraints.
Accessibility and Travel distance proxy
Two families of indicators are computed on the finished network. The accessibility indicators give, for every populated grid cell, the travel time and the network distance to the nearest settlement of a given type or to the nearest centre of a given rank. The travel distance proxy runs a spatial interaction model over all origin and destination cells within 60 minutes of each other, and reports potential accessibility, average travel distance and average travel time per origin, plus the modelled traffic flow assigned to each road link. Those link flows are sampled back onto a fine grid and split by road class, which is the form in which they are delivered to emission modelling work.
The Model mechanics section describes each of these steps in more detail.
The model runs on the open source GeoDMS platform. The configuration in this repository has been run with GeoDMS 18.1.2. Because the network of a full continent is held in memory during routing, the requirements are substantial: a recent Windows machine with a large amount of RAM, or a very large page file, plus fast local disk for the intermediate .fss files. Some of the largest countries (China, India, the United States) do not fit in one run and are handled by splitting their origins into smaller functional areas.
Most work is not done interactively but through batch scripts that call GeoDmsRun.exe for one country or one continent at a time. See Tutorial for how to obtain the data, set up the configuration, and run the model, and Model parameters for the settings that control a run.