I believe it's a population based percentage. However, there is a global map on page 15: https://www.stateofglobalair.org/sites/default/files/soga-2018-report.

I believe it's a population based percentage. However, there is a global map on page 15: https://www.stateofglobalair.org/sites/default/files/soga-2018-report.pdf https://www.stateofglobalair.org/sites/default/files/soga-20...