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I am trying to find out which green belts in a city are situated below (or almost on the same height as) the roads. I have a shapefile of all the paved roads and also a shapefile of the green areas. Also, I have a raster of 0,5m with the height values of the area.

First of all, it is important to know where the road and green belts adjacent. Therefore I did the following:

  • Created a buffer around the green
  • Created a buffer around the roads
  • Used intersect to find out where they overlap/adjecent

Next, I calculated the slope on the height raster and clipped this to the intersect vector layer that I just created. I now know how steep the slopes are on the areas where the green and roads meet. This is useful, but I think using a slope is not the best solution. This because I can now filter on areas where there is no to little slope which allows me to find the areas where green and road are almost on the same height. However, it does not really reveal the locations where the green belts are necessarily below the roads and also doesn't show by how many centimeter they are lower.

That is why I am trying to find a way to extract the height values of the cells where the green and the road adjacent. This might be a long shot, but if you know how I could solve this please let me know!

I use QGIS.

  • Try using the Zonal Stats processing tool to calculate the average elevation in each zone. – csk Jul 15 at 21:49
  • Thanks! I already tried this, but the problem with this tool is that it calculates the average for a relatively large area. This makes that technique less accurate unfortunately. – Jozef à Nijeholt Jul 16 at 6:45
  • What do you mean by "relatively large area"? Isn't the area defined by the size of the zone polygon? – csk Jul 16 at 15:14

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