How were these GPS points obtained?
Data on Eskom's power plants comes from their site. The City's power plants was found by combining sources (City's website, Google Maps, etc).

Are there any known data gaps?
The exact status of the Athlone power plant should be verified. The main plant was demolished a while ago, but a small generation unit is suppose to have been set up. This should be confirmed. Also there is only basic info for Cape Town-owned plants and this should also be added to.