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I'm trying polygonize the elevation level 200 m of Europe map from raster GeoTIFF (The raster is projected in EPSG:3120). At first I tried with Raster > Extraction > Contour, but the lines are interrupted in many parts so using lines to polygon didn't convert it well, joining the line at interrupted path. Then I tried with Vector geometry > Polygonize which in some cases created the polygons but in the major part of the map couldn't create polygons. After that I thought to try it directly from raster using at the process toolbox from GDAL > Raster conversion > Polygonize (Raster to vector), this took about 24 hours and didn't finish the process so I canceled.

I'm stuck at this point. The other elevation levels (500m, 1000m, etc) looks fine. Maybe they have less data than 200m. Can someone tell me whats wrong or a solution for this ?

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  • you might be better of using vector data, example openmaptiles.com/downloads/dataset/contours/europe/#9/66.4981/… has contours for europe (14.85GB download).
    – Mapperz ♦
    Commented Dec 8, 2019 at 18:52
  • well i think that i have a different area of Europe map bigger then openmaptiles bounds and need to download Asia and Africa continent too, so the data its too large just for lvl 200m contour.
    – Iven Pepa
    Commented Dec 9, 2019 at 19:13

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One possible workaround can be creating a new raster with the raster calculator and the following formula:

("Slopes@1" >= 200) * 200"

Assuming that Slopes is the name of the source raster, the output will be a raster with pixel values 200 for source pixels values greater or equal than 200, and zeros for the rest.

Then you can poligonze that raster.

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  • I'm sorry for late response, i'm trying this formula ("Slopes@1" >= 200) * 200" but the result its empty view prnt.sc/q8h2w3. I did raster calculator > ("Slopes@1" >= 200) * 200" > select layer. I tried another way before, simple formula "Layer name" < 200 and the output was as i wanted prnt.sc/q8h519. As you can see there are too many small areas. Ill try to delete after polygonize using vector>geometry tools>add geometry attributes and deleting the assigned area. But as i said it took 24 hours and didn't finish the process, so i canceled.
    – Iven Pepa
    Commented Dec 9, 2019 at 19:44
  • You say that take 24hs with the original raster. This is a raster with only two values. Can't take 24hs for that.
    – Gabriel De Luca
    Commented Dec 9, 2019 at 20:06
  • I don't remember in which layer used polygonize. Just to be sure I'm trying this now and still waiting. I'll let it till tomorrow. Hope to get some correct result.
    – Iven Pepa
    Commented Dec 9, 2019 at 20:14
  • After 3 hours and 30 min finally got the level 200 elevation polygonized. Thank you Gabriel
    – Iven Pepa
    Commented Dec 10, 2019 at 19:40
  • You are welcome Iven. I'm glad it worked. The detail of the raster was really too much.
    – Gabriel De Luca
    Commented Dec 10, 2019 at 19:48

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