Hey IcyFox, sorry to tell you your map has been rejected.
The build is decent, it's attractive but a bit plain and obviously there's nothing on the other side of the walls. The theme is unoriginal because there are already a lot of city-themed maps, and even one called "City" (City). The parkour isn't great either, because it's pretty repetitive (you use mostly normal blocks- try to use a good variety like panes, soul sand, vines, etc.). It's also a bit easy for a Medium.
Thanks for submitting, I'd love to see more maps from you!