I'm working with QGIS 2.6

I have a points layer representing different bus and train stops. I applied a categorized symbology; each colour represents a class of value (field regarding time access from a starting point).

I would like represents this time information as different polygons, because in a 2nd time I have to intersect this information with another point layer.

Could you throw a light on this for me? Rasterize this data would be a interesting way? I tried vector -> convex envelope, but the result is not what I am looking for. The spatial distribution of points seems to be too complex to convert the points cover toward convex envelope.

I paste below a SS of my current point data:

enter image description here

  • I'm unclear on what you're trying to do. You mention creating a surface from these points, which would be interpolation to a raster (and if I understand your goal the best option). You then mention making polygons out of them and convex envelope. For that you'd select the points of one class and run it on each, and likely get overlapping polygons. You might be looking for concave/alpha hull, but that's more complicated. You could also do Voronoi/Thiessen polygons on the points and dissolve the resulting polygons with same value, but that will extend some values well beyond their points. – Chris W Apr 8 '15 at 19:48
  • If you really want polygons that outline the area of common class times, I would: Interpolate points to raster using the original values (ie do not classify at this step) possibly using IDW, reclassify the resulting raster with the same scheme you used to classify the points, and then vectorize that classified raster. There may be some cleanup/generalization needed of the classified raster or the polygons that result from vectorizing it. – Chris W Apr 8 '15 at 19:52

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