Maps serve a purpose.
People use it for directions.
They trust it and depend on it to get them where they want to go. It tells them where the local attractions are, and other places if interest, particularly among tourists - the people who use maps the most. These are the two questions that will make the foundation of your business. Big cities are very seldom a great market for City Maps. However, if you break them apart and make maps for selected business districts, even down to selected neighborhoods, the taking is plenty.