Qgis 2.18 English

Points, lines and polygons can be shown in different categories in the map image. This is especially useful when an attribute can only have a limited number of values, such as motorways, types of livestock farms, etc.

• Click on the relevant layer in the Layers Panel

• On the left side of the Layer Properties window, click on the Style tab 

• Choose Categorized in the top-most bar 

• At Column, choose the attribute of which you wish the values to be displayed in the map image

• Choose Classify

• You can adjust colour and colour ramp 

• By clicking on the symbol in the window, you can adjust this too

• Click on OK

You can have Qgis classify the attribute values of points, lines and polygons of a vector layer and have these displayed in the map image in different colours.

• On the left side of the Layer Properties window, click on the Style tab

• Choose Graduated in the top-most bar 

• Choose Colour at Method 

• Choose a Colour Ramp or click on Edit to make one yourself 

• Choose a classification method and click on Classify

• Click on OK

By this you can show the size of a particular value within a vector layer. To this end, Qgis creates a number (indicated by you) of classes. These can be seen in the map image as symbols (such as circles, stars, etc.) of different sizes.

There are several ways for the different types of data: 

Points

A file containing point data can be given different symbols and also symbols of different sizes. 

• Click on the relevant layer in the Layers Panel
• On the left side of the Layer Properties window, click on the Style tab 
• Choose Graduated in the top-most bar
• At Column, choose the attribute whose values you want to determine the size of the symbols
• Choose Size at Method 
• Choose a size in millimetres, pixels or map unit
• Choose a classification method and click on Classify 
• Click on OK

Polygons and diagrams  

• In the Label Toolbar, go to Layer Diagram Options (or open the Layer Properties window and click on Diagrams) 
• Choose Pie Chart at the top 
• At attributes, choose the values you wish to be displayed in graduated symbols (e.g. number of residents) 
• At Size, choose Scaled Size 
• At attributes, fill in the values again that you wish to be displayed in graduated symbols (so, once again, the number of residents as in our example) 
• Behind Maximum Value, click on Find 
• At Size, choose an appropriate size for your map image (try a few) 
• Click on OK

Polygons and centroids

In a vector layer consisting of polygons with statistical data per area in them (e.g. per municipality), you can also have these data displayed in graduated symbols. To this end, you will first need to make a layer containing the centroids:

• In the Layers Panel, activate the layer whose data you wish to symbolise
• In the Toolbar Menu, go to Vector and choose Geometry Tools
• Opt for Polygon Centroids
• Create a new layer and name it or opt for a temporary layer
• The layer that is activated will be presented as Input Layer; click on Run 
• Now click on the newly created layer of centroids 

Style your centroids as you would style a layer of points: 

• On the left side of the Layer Properties window, click on the Style tab 
• Choose Graduated in the top-most bar
• Choose Size at Method
• Select a size in millimetres, pixels or map unit 
• Choose a classification method and click on Classify 
• Click on OK