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I'm new to QGIS and am trying to create vector contours from this IDW raster. I followed Ujaval Gandhi's "Interpolating Point Data" tutorial step by step but am not getting the same results for step 18.The first images is the IDW raster. The second is the contour vectors created from raster->extraction->contours which looks like it created a point for every pixel in the raster.

IDW raster contours vectors

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    Please edit and add a link to: Ujaval Gandhi's "Interpolating Point Data" – dof1985 Jul 25 '15 at 19:40
  • Please clarify your question. The screenshots dont look like "a point for every pixel". – underdark Jul 25 '15 at 20:50
  • correction - duplicate of this question : gis.stackexchange.com/questions/155658/… – Steven Kay Jul 25 '15 at 23:23
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    What contour interval did you specify? What is the range of values in the interpolated raster? – whuber Jul 26 '15 at 16:34
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    Here's how I came up with it: a contour map will be readable and useful only when it contains between a few and a few dozen contour levels--roughly around 10. Dividing the range by 10-1 = 9 gives very close to 10000 for the common difference between all contours. I don't use QGIS, but I would hope its interface would suggest a default contour interval using a similar rule--and that it would issue a warning when asked to generate a ridiculous number of contours (say, over 500 or so, which would allow only one or two pixels between contours on the screen). – whuber Jul 26 '15 at 19:29

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