What is the setting of The Dark Tower VII: The Dark Tower by Stephen King?

The Dark Tower VII: The Dark Tower, is primarily set in two worlds: the Keystone World, or the real world, and the world of Roland Deschain, Mid-World. The characters move back and forth between these two worlds through the use of doors, and are largely unseen by the greater population in the real world. The Keystone World is considered the real world during the latter part of the twentieth century.