I have a love of historical maps and Voommaps 1934 copy of Gregory’s Sydney Directory provides a great resource for creating a rich gaming world based in reality. As a game master, it saves me a huge amount of time to have this available to fill in the blanks. Adapting the map to a Steampunk world, or a pulp adventure story set in the 1930’s.
This provides a great example using a single map resource. There are many more examples out there if you look beyond Sydney. Maps of London from the 1700s, maps of Paris going back to Circa 360. These can act as inspiration, player resources, or a backdrop to the world.