A domed city is a type of city that has a big roof over it. It's kind of like a big dome you've probably seen at a sports stadium, but much bigger and more permanent. The roof is usually made of glass or metal, and typically covers an entire city. This roof helps to protect the people inside from bad weather, like rain or snow, and can even help to keep the city cooler in hot weather. The roof also helps to keep out noise, which is especially important if you live in a busy city.