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I am trying to make a depth map of a lake. I am using the contour plugin to generate contour lines. The problem I am having is that when I use the plugin the contours come out right except on the north side of the lake. They do not follow the outline of the lake on that side. I am not sure how to go about making the contours only show up inside of the lake. I have added a few screenshots of what I have.

I am not a master GIS user. I am a fisheries biologist learning to use QGIS.

This is the outline of the lake. I only want the contour lines to show up inside the lake.

This is currently how the contours are showing up.

PolyGeo
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Chad Washington
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  • Can you share your depth dataset on a file sharing site? Then it would be easier to find a solution. If it is under a commercial license, could you find an other sample data source? – Gabor Farkas Oct 17 '14 at 14:20
  • yeah I can do that. Have a site you recommend? – Chad Washington Oct 17 '14 at 14:30
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    At this point can you just clip the contour lines to the shape? Based on a quick look at that plugin, I don't see a way to set any perimeter rules, and by default it's going to interpolate within the convex hull of all the points--what you have there is a concave hull. – elrobis Oct 17 '14 at 14:49
  • Would it be worth seeding the point file with some land elevation values on the north side to improve the dataset available to the interpolation algorithm, then clip the dataset afterward for a more polished product? – elrobis Oct 17 '14 at 14:55
  • I have tried clipping it with the lake outline shapefile but it never comes out right. I may be doing something wrong though. – Chad Washington Oct 17 '14 at 14:57
  • @Chad Washington, there is an article about the most popular ones: http://www.ebizmba.com/articles/file-sharing-websites – Gabor Farkas Oct 17 '14 at 15:33

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