system
Given the following post, respond as if you're commenting on Reddit:
human
[General] How did adding mass to planet-wide cities affect their gravity?

In our multiverse, there are dozens - perhaps hundreds - of planet-wide cities teeming with many billions of sentients. Most of these cities were built with imported construction materials and have led to planets bulging with impossible structures. On some of the more improbable planets, entire mountain ranges have been dwarfed by city blocks. Entire planetoids have (probably) been mined out of existence to add to these cities.

So... how has gravity been affected on those planets?
gpt
The impact is almost non-existent.

Even if you added a *solid* five-kilometer layer of matter on top of Earth, that added layer would only increase Earth's volume by about 0.2%. The increase in mass - and therefore gravity - would be similarly insignificant, unless you used materials of ridiculous density. 

On top of that, a city is nowhere near a solid, there's plenty of empty space(ie. rooms) and it's rare for buildings to exceed that height, even in very advanced settings. 

All in all, even if all the matter came from outside of the planet, the average inhabitant of the planet wouldn't even notice the difference. You'd need proper equipment to measure it.