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I'm looking for a way to create a buffer from a specific point that represents the catchment area in a selected time in QGIS. I've found many tools that allow me to do it using driving time or public transport. I need to do the same only using walking time in a natural environment using the geophysical information of a DTM as criteria. More in detail, I'm trying to reconstruct the catchment area of some different roman period settlements and to do that I'd like to create some isochrones of different walking times. I've searched all over the web but I have not been able to find a solution to this specific problem. I've spent time trying to use SAGA algorithm of Accumulated costs but somehow I'm not able to run this tool. I hope someone could help me or suggest me a proper tutorial.

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you could use the r.walk.coords GRASS algorithm using processing (available in 2.18, may not be available in older versions).

According to the documentation this uses Naithsmith's rule which iant mentioned. It also takes into account the varying cost of uphill versus downhill for different slope ranges.

Not used it myself, but it looks like it'll do what you're after.

You'll need to create an additional friction raster (e.g. you could rasterize polygons for wooded areas to make walking progress slower through forests), although I suspect you could set all the cells to zero if you only have a DEM.

  • Thank you and also thank to Iant. I've been able to do that, just neded to spand some time setting properly Grass and understanding how to create a usefull friction raste. Now it works well. Many thanks again – Manuele Putti Mar 14 '17 at 15:09
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You need to apply Naismith's rule to your terrain model. Fritz and Carver did something similar in this paper and with See combined it with Dijkstra’s algorithm for routing in this paper (pdf).

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