How can I create contour lines that are filled with a graduated symbol usinq QGIS?
In ArcGIS for Desktop I can do this. What about in QGIS?
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I've done it by styling the geotiff image based on the pixel value.
By default, the geotiff looks gray. So I go to Properties (right click the layer in leftside panel), and in the 'style' tab, select 'Colormap':
In the Colormap tab, I add a bunch of entries. In my geotiffs, 'nodata' has been replaced with a zero value (indicating buildings theres) which i set to black, the rest is scaled up colorwise based on the pixel value (950 = 9.50m above sea level.
For nice maps, find the upper and lower bounds first, and use Colorbrewer to find a nice color ramp. A bit of effort at first, but can save the style:
I set it to 'discrete', so it goes by steps. If done every meter, you could mimic the contour lines like this, albeit it less smooth then the calculated ones would/could be. Depending on what you need the map for, you can make the colors move gradually in between by setting it to 'Linear'.
Given I combine it with other data, I then went to Transparancy tab, set 50% transparancy, overlayed it on a base map, for this result:
You may notice: - on the low end my range estimate was off, as there's ALOT below my lower bound which should be split up more. This is however just for the sake of the example pictures. - Deliberately taken screenshot at the end of the map so you'd see the overlay. - All data used here is data provided by AGIV (GRB Vlaanderen WMS + DHM Vlaanderen, raster 5x5m) and is not to be spread without mentioning source of data.
I wrote this article which discusses the different options for contour maps in QGIS.