From My Little Wiki
Cloudsdale is a city in Equestria that is featured in the TV show My Little Pony: Friendship is Magic.
Cloudsdale is a floating city in the skies of Equestria. It is exclusively a home for Pegasus Ponies, the only race that can fly and walk on clouds. However, Earth Ponies and Unicorn Ponies can travel there if aided by magic spells that let them walk on clouds. Cloudsdale is responsible for much of the weather produced in Equestria, and most Pegasi appear to work in weather-related jobs.
Cloudsdale is also the original hometown of Rainbow Dash and Fluttershy.