Need recommendation: software for creating landscape? Scenes?

Don't quite know how to describe what I'm looking for, but it's NOT 3-D game design, or creating new worlds, or anything like that. I'm writing a book, and just for my own purposes, I would like to be able to "create" for example a city, lay out the streets, add buildings, etc, or a ranch, or similar. Just be able to say ok, I'll put a little grove of trees here, and there'll be a pond over here; no, that's too big....let me just make that pond a little smaller...... etc, etc.

Does such software exist, and if so, will it have a really steep learning curve?

Thanks for any advice!