Road lengths

This is the simplest of the analyses: how many kilometres of road of each class are there in each grid cell. It is computed straight from the initial road segments, not from the compressed network, since the question is about the physical network rather than about routing.

The configuration is Analyses/RoadLengths.

The computation

Per continent, the segments of the initial working network are taken, each with its length in Web Mercator metres and its main road class. Every segment is walked at a fixed step of 100 metres with dyna_point, which turns a line into a series of points at regular spacing.

Each sample point is projected to WGS84 and assigned to a cell of the output grid. Its weight is 100 metres, except for the last sample of a segment, which gets the remainder of the segment length so that the total weight over a segment equals its true length.

Summing the sample weights per grid cell, filtered by road class, gives the road length of that class in that cell.

Output

Per continent, to %LocalDataProjDir%/RoadLengths/<continent>/<class>.tif, with one raster per main road class: Main, Secondary, Tertiary, Not_A_Road and Connector. In practice only the first three carry meaning; Not_A_Road is empty because such lines never enter the network, and Connector holds the artificial links that attach origins and destinations.

The continental grids are summed into global mosaics in %LocalDataProjDir%/RoadLengths/_all/, as main.tif, secondary.tif and tertiary.tif.

The output grid is the same 100 metre WGS84 raster used by the flow grids of the Travel distance proxy, which means road length and modelled flow can be compared cell by cell, for example to derive a flow per kilometre of road.