Sci-fi worldbuilding ideas for your city planets :)
If the planet is entirely city, where does the oxygen come from? Are their farms dedicated to producing oxygen? Special factories? Are there plants that produce oxygen very quickly all over the planet? Do you have to pay an oxygen tax?
Does the planet have natural water? Are the oceans untouched, incorporated into the city, or have they been drained and the water used for things in the city? What is it used for? Drinking, dams, hydroelectricity, food production, etc?
How deep does the city go? Has the planet been mined into to create more space? Is geothermal energy used? Are the bottom levels reserved for things such as sewage, electricity production, factories, prisons, etc?
What is transportation like? Are there roads, floating roads, or are trains and trams used instead? Are planes used? Is transportation fast enough to quickly travel across time zones?
How is food produced? Is it imported, or is it grown on planet? A combination? Think about greenhouses, factorised farms, vertical farming projects, etc. If oceans are left relatively untouched, is food produced in it? Are fish kept? Are there ration laws?
Are the poles less occupied than the rest of the city? Are they used for storing frozen goods, super computers? On a planet with no oceans, is ice and snow valuable?
The same goes for the equator of the planet. Is it more or less occupied? Is the heat used for anything? Are there solar panel farms? Air conditioning?
Are there parks and protected areas of nature? Ancient gardens, important forests, sacred land? Are there laws about chopping down trees? Are there farms for trees and plants? Are their plant shops, and are they expensive? In Star Wars, a part of Coruscant's highest mountain is a public monument that you can look at - are parts of mountains, rare ores, fossils, etc, preserved?
Not all sci-fi cities look the same. Coruscant has skyscrapers arranged in a very chaotic manner, stretching incredibly deep and incredibly high, and there is almost no plant life or natural parts of the planet to be seen. Xandar is arranged neatly with very similar style buildings whilst remaining relatively low rising compared to other city planets, and has lots of greenery and a fairly untouched ocean. Wakanda is relatively defined in layout, with a mixture of plants and buildings, houses and skyscrapers, with every building being unique. Draw inspiration from whatever you like.
Write whatever you want, even if it's common or cliche. It doesn't matter if it has been done before, because it hasn't yet been written by you.
Happy worldbuilding!
