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Using QGIS to make custom Contour Maps

Tudor -

We get a lot of requests for contour maps. The issue with automatically generating contour maps is that there is no way to do so without making a lot of assumptions about what the user wants. Contour interval, coloring and what the contours are displayed over are all things that need user input. 

Making a contour map based on the DEM that Maps Made Easy generates by default is both easy and fun and allows for all sorts of customization. But beware... You might have to learn something!

 


 

In this example we will make a contour map with black isoelevation lines every .5 meters and some customized coloring like this:

The data we are working with here is the sample DEM that is generated with our sample data set.

 

 

First, you will need the Quantum GIS (QGIS) software which is free. Download it from QGIS.com and install the latest version.

Next, you will need to download the DEM GeoTiff from your Map Detail page. 

Open QGIS and open the DEM. To do this, go to the "Layer" at the top, select "Add Raster Layer" and select your DEM file. A "Raster" just means a pixel-based image.

 

Now your DEM GeoTiff will be shown in the main window. The lighter the area, the higher the elevation of that area.

 

Now open the Properties for the DEM by right clicking on it in the "Layers" panel and selecting "Properties".

 

To do the custom coloration choose the "Style" menu on the left of the "Layer Properties" dialog window and do the following:

  • Change "Render Type" to "Singleband pseudocolor"
  • Choose a color map in the "Generate new color map" section. "Spectral" is the default.
  • Press the "Classify" button. This will fill the colors and values in on the left.
  • Hit OK.

 

 

After changing the color map the image will look like this:

 

 

To add the contour lines we will open the "Raster" menu at the top and select "Extraction" and then "Contour".

 

The Input file will already be selected. Fill in a name for the "Output file for contour lines" and edit the "Interval between contour lines" to .5 (or whatever you want). Hit OK a few times and it will generate a shapefile that contains the contour lines.

 

Now contour lines will be shown at the prescribed interval but the coloring will be a random color.

 

To change the coloring of the contour lines right click on the newly generated layer in the "Layers" panel and select "Properties".

 

On the style screen click the color selector and select black. Hit OK.

 

Here is what the final product will look like.

 

 

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