4. Style Rivers using the Interpolated Line Renderer
Now we're going to style the rivers. We would like to see the width of the lines increasing from upstream to downstream.
1. Hide the basin polygons by unchecking its box in the Layers panel.
Let's have a look at the attributes of the rivers layer. Because the attribute table is large, we're not going to open it to see the attributes. That will take a lot of time. Instead, we'll use the Layer Properties.
2. In the Layers panel right-click on HydroRIVERS_v10_eu and choose Properties... from the context menu.
3. In the Layer Properties dialog go to the Information tab and scroll down to the Fields section.
You can find the description of these fields in the PDF that came with the downloaded data. It is always important to read the metadata documents to understand the data.
We can use the ORD_STRA field, which contains the Strahler orders.
4. Click OK to close the Layer Properties dialog.
5. Go to the Layer Styling panel and verify that HydroRIVERS_v10_eu is the target layer.
6. Click on Simple Line.
7. Change the Symbol layer type to Interpolated Line.
8. In the Stroke Width section change FIxed Width to Varying Width.
9. For Start value and End value choose the ORD_STRA field.
10. Click to automatic set the Min. value and Max. value between which it should interpolate the line width.
11. Set the Min. width to 0 and the Max. width to 1 mm.
Now we've set the varying size, but we also want to vary the color.
12. Scroll down to the Color section and change Single Color to Varying Color.
13. For Start value and End value choose again the ORD_STRA field.
14. Click to automatic set the Min. value and Max. value between which it should interpolate the line color.
It looks already nice with a blue ramp, but in the next section we're going to blend it with the basin polygons. Therefore, it is necessary to change the ramp to gray.
15. Change the Color ramp to Greys.
In the next section we're going to blend the two layers.