How to produce opposite semicircle maps in CARTO or QGIS?

Question

I need to produce a map of opposite semicircles or concentric circles to represent two numerical columns on the same map simultaneously. I have already tried to create a layer for each column's data and simply overlay it in QGIS. However the data ends up covering each other. The ideal would be to have different circles at the same point (concentric, but not overlapping) or opposite semicircles.

Objective: I want to create a map that compares an event in two different years but in the same place. So a semicircle would represent 2019 and another 2020.

I don't know if abroad this type of map carries the same name, so follow two examples:

![ source: []1http://www.uel.br/cce/geo/didatico/omar/pesquisa_geografia_fisica/Construcao_LeituradeMapas.pdf]2

I'm a student so I need the tools to be free. I only know how to work with QGIS and CARTO, but I can learn other tools as long as they are free.

Answer 1

1. Set your layer styling to Graduated based on your first field, and set the method to Size.

2. Click Classify to set your symbol size class breaks. Make note of this classification!

2. Open the Symbol Settings and select the Simple marker in the list of symbol layers. Set this to the half-circle symbol style, and choose your desired color.

3. Right click the layer in your layer list and click Duplicate Layer.

4. Open the layer styling for the duplicated layer. Set the graduated symbols to refer to the other field you want to compare. Make sure the classification is the same as the other layer!

5. Go into the Symbol Settings on this layer. Set the color to something different, then set the rotation to 180.

That should do it! You could also play around with the geometry generator to accomplish this in a single layer.

Also, if you wish to have a legend item that is the circle outline, you can create another copy of the layer and set the symbol to hollow circles, then use that layer for your legend.