Cartographers are selling maps to mansions I've been at.  I have a custom built village where I created a cartographer who sold me a map.  The map led us to a new mansion.  After that mansion we continued heading away from home and found a village with no cartographer.  We placed a cartography table and made a cartographer.  Traded him up to sell a map, the map brought us to a mansion we have already been at.  Left that mansion and again headed away from home until locating a village.  Created a Cartographer and traded him up to sell us a map.  This map also brought us to a mansion that we already explored.

I have visited approximately 20 Mansions in total on this map since they were released in 1.11

This world was originally created in 1.8