I guess I prefer my fantasy a little darker - this optimistic production, somewhat utopic in nature, would not fit in my games. That said, in a more cheerful campaign, PCs could easily be part of the Royal Surveyors Guild, on missions to collect the information for this publication. Such an easy source of hooks to send them on any number of crazy missions for no other reasons than to see what is there.
This would fit in where your campaign had posted want ad's or adventurer's guilds.
All hell breaks loose when a new mayor/governor takes over, perhaps with fresh siege experience, and decrees that the Wall Line must now be enforced. What havoc will follow when the guards come in force to clear the 'debris'.