A new feature in Google Maps for Android 6.0, is the support for floor plans in buildings:
When you’re inside an airport, shopping mall or retail store, a common way to figure out where you are is to look for a freestanding map directory or ask an employee for help. Starting today, with the release of Google Maps 6.0 for Android, that directory is brought to the palm of your hands, helping you determine where you are, what floor you’re on, and where to go indoors.
The result looks like this:
You can also add your own floor plans, via a web interface: