I am lost in the spaces of my books. Actually, I keep finding more and more questions about my world that I have to answer. It’s much easier to put your story in modern day United States, because the reader knows how things work and what cities are like, so you don’t have to explain about a lot of things.
If you build a world from scratch, you have to figure out how all the systems work and make them realistic, based on physics and our world. That is, for science fiction. In fantasy, you can do anything you want, and call it magic, as long as it’s consistent.
Sam’s world is morphing from a totally covered city-world to one where other sectors have open forest and one tribe of aliens lives in trees. Only the trees are going away. Sam’s city is going away and people won’t leave.