Writing a draft is like making a map. What you are mapping is up to you.
If you imagine yourself outside, you will test roads, find crossways and connections, name streets, and never be satisfied with what you've been told about a place. You will go down ill-used paths until you can look beyond the flat edge of the end of the world---here be dragons!
If you see yourself as map-making inside, you will knock on closet backs to check for hidden passages, tear down walls if you suspect doors behind them, and crawl into tight spaces. You will measure a room in the steps of your character. And lie down on your back to examine the ceiling.
Why?
Because then you will lay out your findings in an organized way so that others may explore the same paths, see things they didn't know were there, visit little known attractions, discover short (or long) cuts, realize one land lies beside another, and perhaps find a trapdoor to a populated underground or a ladder to a long undisturbed attic.
You're asking your readers to risk a mountain because you named it and marked one route. I've dared valleys because someone has gone in before me and assures me they will lead me out. Even a house that I've been inside a thousand times is worthy of rediscovery when someone hands me a floorplan and tells me the history of how the backstairs were added.
Fellow blogger Jennifer Thermes is reading Mapmaking with Children: Sense of Place Education for the Elementary Years and has Maps of the Imagination: The Writer as Cartographer on her TBR pile. Jennifer creates maps for a living.
What's the last map you drew? Why?
P.S. I love a good map in a book. Do you? Here's a blog post from The Map Room devoted to Imaginary Places.