For citation here are two sources:

50% of population: https://ourworldindata.org/urbanization#how-urban-is-the-wor...

70% of emissions: https://www.c40.org/why_cities

This is based on the concept of a "consumption emission", which is an interesting concept. The point being that cities (especially western cities) have seen their emissions drop due to de-industrialization, but consumption has increased (hence your statement about carbon footprints correlating to wealth/income). To say that cities impacts are smaller when they just outsource all of their carbon impact is disingenuous.