4.1 Exercise content

This exercise familiarizes you with visualization techniques for vector data.

4.2 The goal of the exercise

After this exercise you know how to use basic visualization tools for different data sets.

4.3 Preparations

Open a new QGIS project (Project > New) and save it as “QGIS-exercise 3”. Add the following data to the project:

• ..course_directory/geofabrik/berlin_placenames.shp
• ..course_directory/geofabrik/berlin_roads.shp
• ..course_directory/geofabrik/berlin_water.shp

4.4 Visualizing vector data

Take a look at all the vector data sets that are currently open in your project. You will notice that on the left side of each layer there is a shape that describes its vector type. berlin_placenames is a point data set, berlin_roads is a line data set and berlin_water is a polygon data set.

4.5 Visualizing line data sets

In the Layers Panel, set the berlin_roads layer visible and hide all other layers. Right click the berlin_roads_layer in the same panel. Navigate to the layer’s Properties and select the Symbology tab like we did with the raster data set earlier. Note that the properties of a vector layer are more complex than those of a raster layer. The Symbology tab is completely different as well.

Specify the width and color of the berlin_roads layerand press Apply to update the map view with your changes. Now, select a line style library, Favorites for example, and change the line style to one of the options. Once done, press OK to close the window and view berlin_roads visualized with your symbology settings.

The visualization of other geographic data sets follows the same pattern: Right clicking the layer, selecting Properties… and then the Symbology tab. Different types of vector layers (points, lines, polygons) have different symbology properties. Although the appearance of the symbology tab is quite similar when working with vector data, you cannot style a line layer with the exactly same symbology settings you used for a point layer, for example.

4.6 Visualizing point data sets

Let’s visualize point data next. Set the berlin_placenames and berlin_roads layers visible and keep other layers hidden. The placenames layer has Berlin’s place names as points (data from OpenStreetMap / Geofabrik). Open the layer’s Symbology tab just like before and notice the differences between the properties of line and point layers. Select a new Color and Size for the symboland press Apply. Change the symbol itself as well and try how rotation affects the appearance of the symbols.

Your point and line data sets together could look something like this, for example:

4.7 Visualizing polygon data sets

Let’s move on to polygons. Set the berlin_water layer visible together with the berlin_roads and berlin_placenames layers and hide all other layers. Open the symbology tab of the berlin_water layer and note the differences to the properties of the previous point and line data sets. Experiment with colors and selecta different symbol for the layer. Feel free to try different opacity values as well. Once you have tinkered enough, press OK.

It is possible that your layers overlap in such a way that for example some of your points are left invisible underneath the water polygons. You can fix this by editing the layer order: simply drag the layers into your desired order in the Layers Panel. It is often best to leave polygon data sets at the bottom. Same goes for raster data. Your rearranged vector layers should look something like this:

4.8 Changing symbols

Next we will change the symbols of the polygons. Open the properties of the berlin_water layer again and from the Symbology tab select the Simple Fill line:

Now set Stroke style to Dash Line. You can also set the Stroke width to your liking. Finally, set the Opacity to 70%(From the Layer Rendering settings).

4.9 Scale dependent symbols

Next we will set a scale limit for the berlin_placenames layer. Select the layer’s Properties > Rendering and check the box Scale Dependent Visibility. Then set the Minimum to 1:200 000. With this setting the place name layer is visible only when the scale is larger than 1:200 000.

Enable your changes by pressing either Apply or OK. The latter closes the Properties window in addition to enabling your changes. Now try zooming the map view and see how the layer vanishes once you zoom out far enough. You can change the scale of the map either by scrolling with the mouse or by typing the desired scale into the scale section of the Status Bar at the bottom of the screen.