QGIS - Plugins, Processing toolboxes and Groups

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1. Plugins

GIS systems will provide you with a lot of toolboxes to process your data. QGIS is written in python and you can even write your own plugins if you like. Sometimes, the toolbox you want to use is not included in the basic installation. The toolboxes we use in this exercise should already be available with the basic installation, but if you can't find them, you can search through the plugins.

1) To add a Plugin, select from the top menu "Plugins -> Manage and install Plugins."
2) The popup menu shows you the installed plugins and available plugins. If a plugin is not in the official database, you can also install it from a zip file.


2. Processing tools

In the top menu, click on "Processing -> Processing toolboxes." A window will open on your right-hand side showing all available toolboxes. Let's do two calculations: slope and contour lines. Some toolboxes are also available in the top menu, based on the data type you have. As the DEM is a raster, you would find according tools here.

2.1 Slope

1) For the slope, we use the "Processing toolboxes." Search for "slope" and select the toolbox with the little blue cogwheel.
2) Select the DEM (large or subsets) as the elevation layer and set the Z factor to 1. Click on the three dots and select "Save to file...". Select a path and a file name. Then click on Run; it may take a moment.
3) The result shows you the slope of the mountains in degree.


Now that we have done our first calculation, let's give it a meaningful color-scheme.

1) In the "Symbology," select
  • Render type: Singleband Pseudocolor
  • Interpolation: Discrete
  • Label precision: 0
  • Mode: Equal intervals
  • Classes: 3 or 5
Find online the main degrees for avalanche steepness. Sometimes you can also find some more division. Choose either source and set you values accordingly. Choose red, green and orange as colours. The result should look like this:
2) In the colour menu, use the html notation to get the exact same colour for similar groups. In the case of the image above, too steep or too flat slopes have the same green colour as avalanches are unlikely (either because it is too flat or because they are so steep that not much snow will accumulate.)
3) Your result should look similar to this map.


Save your project.

2.2 Contour lines

Contour lines are a very important tool in cartographic. They display lines of equal height and you can "read" the terrain by looking at them. Let's calculate slopes for our DEM.

1) This time, we choose from the top menu "Raster -> Extraction -> Contour."
2)
  • As the input layer, we choose the DEM (or the subset).
  • As an interval we choose 100.
  • Choose a file name.
  • Press "run."
If you don't display the steepness, it should look like this.


3. Groups

If you look in the layers section, you can see that it starts to fill up. A good way to manage many data sets is to group them.

1) Press on the icon that says "Add group"
2) Create groups and subgroups to your liking.


Good job, save your project and let's move on.