I am doing bathymetry analysis, where I would like to color the contours one by one in the case land is rising (or sea level going down). There is a comprehensive explanation about coloring contours (Colouring areas between (vector) contours?) but it is not working since my contours never meet. I didn't success to change the .shp file with one contour to polygon correctly: I wanted the "land side" of the contour to become polygon, not other way round.

I have several .shp files of contours about the sea bottom topography, but the proper visualization is still missing.

I am using QGis 2.2.

  • Do you have access to DEM that was used for generating the contours? – user30184 Jun 10 '14 at 14:02
  • Yes, well I made contours out of .xyz -data after interpolating the data smaller. But I can make a dem a well. – Laura Jun 10 '14 at 14:13
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    Perhaps you should have a try with gdaldem tools and color-relief and color the DEM directly instead of trying to color the areas between the contour lines gdal.org/gdaldem.html. See also blog apollomapping.com/blog/gdal-color-relief. But you can also open DEM into QGIS and classify it with pseudocolors gistutor.com/quantum-gis/19-beginner-quantum-gis-tutorials/…. – user30184 Jun 10 '14 at 14:24
  • Thanks for advice, I'll check out the gdaldem tools. I am still wondering, though, how is it then possible to separate specific area out of dem (or interpolated -asc file) to color it when there is no attribute table to make sql query? I've already done a layer about sea areas where different depths has their own color. – Laura Jun 11 '14 at 6:55
  • Am I right in thinking you wish to have depths of (say) 0 to 10 metres in one colour, depths of (say) 11 to 20 metres in a different colour, and so on? Like this: dl.dropboxusercontent.com/u/45121071/classified.jpeg – nhopton Jun 11 '14 at 11:21

One fast way for doing visual analysis is to use DEM as starting point and classify it with pseudocolors. You can edit the class ranges and colors etc. to suit your needs.

Styling DEM as pseudocolor

For further analysis you can use the raster calculator. The next screen capture shows how to make a black/white image where pixels with height<10 m are white and pixels above 10 m black. You can continue with gdal_polygonize tool http://www.gdal.org/gdal_polygonize.html and convert this B/W image into polygon shapefile.

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