Location, Size, and Population

Major planetary geographical boundaries, such as mountains, seas, and large rivers, often present natural borders for a region. Depending on its leadership, culture, and the resources available, a settlement might be as small as an arcology floating over a gas giant or as large as a planet-spanning megaplex. In Starfinder, most settlements tend to be larger than the historical cities of Lost Golarion and might cover hundreds or thousands of square miles or span an entire planet. Widespread technological and magical innovations give governing entities wider reach, improve city maintenance, and foster cultural mixing. These settlements are often surrounded by greater metropolitan areas, which might or might not be considered part of the settlement itself.

Populations ebb and flow due to a multitude of external factors. Advances in sanitation, medicine, and agriculture can spur dramatic population growth, while war, economic downturn, or plague can devastate it. A megacity has at least 10 million residents. Megaplexes formed of multiple megacities might have populations averaging 50 million or more. A multi-planetary alliance might have billions or more.

Population size is only part of the equation. Figuring out the ancestry ratios of that population and brainstorming how the members of various ancestries interact can often lead to interesting story ideas, or at least give you some jumping-off points when dreaming up how the settlement was founded and its later history.