Simplify network lead to a bug in GADM shapes

Checklist

• I am using the current main branch or the latest release. Please indicate.
• I am running on an up-to-date pypsa-africa environment. Update via conda env update -f envs/environment.yaml.

Describe the Bug

Summary of bugs:

• Administrative zone is removed in gadm_regions to onshore_regions conversion
• Multiple administrative zones are associated to one shape after simplify_network.

I am running PyPSA-Africa for Nigeria with the GADM clustering option which retrieves GADM shapes also known as administrative zones. See the automatic download: Creating the regions_onshore looks still fine. I am not sure yet what the colour change means. Maybe it is indicating an error? One bug is that black hole inside Africa! Nevertheless, the real bug appears when running simplify_network.py which then creates networks/elec_s{simpl}.nc. As you can see, hovering over one shape, it seems that some shapes are combined.

One needs to debug simplify_network and investigate the step where this occurs. We need to find a solution to this issue.