For one thing, Trantor was the most highly populated of all the worlds, with its forty billion people.
I’m only just now thinking about Trantor’s physical size - if 40 billion people live there, even heavily concentrated, could it be similarly sized to Earth? We have 7+ billion but of course wide swaths of the planet have low concentrations of people and no one lives on 50+% if our surface area that’s covered by oceans. So it seems possible that 40 billion people could habitate the surface area of Earth if the entire planet were as dense as a city. But if not and Trantor is bigger, then it has more gravity, and we’re not led to believe these humans have evolved past current humanity enough to adjust to big gravity differences, and it doesn’t seem like they’ve yet mastered gravitational manipulation since they talk in the previous book about gravitic elevators being a new technology…
