Seven cities in motion
1. A modular city on a series of concentric circular railway tracks. Nobody need commute; you merely wait until your part of the accommodation ring aligns with the appropriate part of the administrative ring, or perhaps sneak through to the entertainment ring inside it or out to the wall ring to look at the mountains. Sometimes an alarm sounds and the rings align in such a way as to avoid or repel a threat from the hole within the innermost track, or from the outside world. Everyone has learned to stay away from the windows when this happens, so who knows what the threats might be.
2. A city of technologically-advanced snails. Having advanced past annexing their shells so that they could bunk up together, they became more ambitious. They formed shell towers, outsourcing propulsion to a small corps of dedicated crawlers, allowing snail farmers and scientists and artists and so forth to dedicate their lives to furthering the survival and knowledge of the snail race. They made glittering atriums and spiral slitherways and triple-horned cornershops and inaccessible, mysterious attics dripping slime down into the city’s highways. Occasionally they visit human cities in diguise as an enormous plate of profiteroles. Always check before you bite.
3. A city in a series of interconnected balloons, somewhere up in the atmosphere of Venus. It has great solar-panel fins to swim it away from Venus’s metallic montaintops. Other than that it blows where the wind takes it, a soft thing in a soft environment. There are others up there just like it, and to a distant observer they might appear to be great wandering jellyfish.
4. A city on an old world, one where every space has been built on and cracked open and knocked down and built on again with the remains of its most recent ruins. The world thus being covered in buildings in greater or lesser states of repair, it falls to us to define a city as its people. These people, banding together in groups of a million or so, roam across this world’s urban deserts year by year. As the climate shifts they move North and South; as the water supplies run out they move onwards; and when the wolves come from the bunkers at night they move their dwelling-places down from the mountains to the sea. In this way the city is constantly on the run. Sometimes it crosses path with another city and splits, amoeba-like, into two hybrid cities heading in diferent directions.
5. A city that was not technically supposed to be in motion, but was swallowed by a fish that refuses to keep still.
6. A city on a monorail. It is a very small city. It currently occupies the third carriage of a train on Line 2 of the Chongqing Metro, and has apparently declared itself an independent city-state. It is not currently a city in motion. The train manager has been called and will attend to the situation shortly. But assuming all that stuff gets resolved in a way that is favourable to the city, it will be in motion soon.
7. A city on a planet that is moving round a star.