I wonder if someone knows a way to calculate time-cost isochrones in a bike road network layer, taking the slope into consideration.

The GRASS tool "v.net.iso" allows to create a line-vector layer with categories depending of how far the roads are from a determinated point. Having the data about the speed allowed me to do the analisys with time-cost categories.

But I would like the analisys to show how slope affects the isochrones: It doesn´t take the same time cycling towards the top of a hill than getting down. So taking the slope into consideration would make the analysis more attached to the reality.

  • what elevation data are you using? Commented Aug 15, 2017 at 10:25
  • I merged a DEM from 416 files (TIFF) and then got the slope
    – Javier
    Commented Aug 16, 2017 at 14:26

1 Answer 1


You could use v.to.db to upload the respective slopes for the vector line segments from a slope map.

Probably you need to split the vector lines into short segments prior to v.to.db using v.split in order to get a realistic representation of the slopes.

Eventually run v.net.iso with cost taken from the slope column (just guessing, maybe the cost column needs some extra data treatment to better represent the cost).

  • I have splitted the network, but could you tell me how to use "v.to.db"? I have not found it within the GRASS-toolbox
    – Javier
    Commented Aug 16, 2017 at 14:24
  • 1
    Weird, it used to be there! Indeed it is "just" a text file to be added. In my Linux box the folder is located at /usr/share/qgis/python/plugins/processing/algs/grass7/description/ but v.to.db.txt isn't there. You could open a wish report at issues.qgis.org/projects/qgis/issues or derived it yourself from an existing other description file (or use GRASS GIS directly).
    – markusN
    Commented Aug 16, 2017 at 18:42

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