Necropraxis' excellent Hazard System doesn't really have a 'urbancrawl' option. The Haven turn presented in it operates under the assumption that adventuring is out in the wild or down in a dungeon. The city is where the characters go to lick their wounds, level up, carouse, and replace their lantern-holder. This is a totally understandable setup. It's a neat nod to Torchbearer's town phase, and I'm sure the writer at Necropraxis isn't trying to say cities can never contain adventures - that's the point of the entire Haven Complications system. And I'm sure Torchbearer could lend itself to urbancrawling as well, though the Grind might be a little less troublesome, depending on the density of taverns.
There are some shifts in tone or mechanic for wilderness turns to become urbancrawl turns. In both areas, encounters mean that NPCs (or animals, or monsters) seek out the PCs. Percepts still involve the PCs seeing the potential encounter, and having more options to avoid it. This is true in both settings, but the difference is distance.
Percepts in the woods work more through implication: wolf tracks, orc droppings, a day-old campfire or three filled with human bones. Cities grind up what we leave behind, beneath our feet. So percepts have to close the distance a bit more.
Nobles will send a foppish bard ahead, or leave behind the quivering, dying body of a commoner who did not kowtow. Thieves will be standing in the open, staring at a character for one instant, then suddenly gone. Guards will tromp up to the PCs and right past them into an alehouse that's behind on its taxes or kickbacks; crashes and drunken yelling jump out the doorway, followed by the thud of a club on some face. Urban settings let percepts brush right up against the PCs, as long as it makes sense, as long as the NPC wouldn't find it odd to see homeless adventurers in their street. Percepts in the wild work more through implication, through increased distance, because it doesn't make sense for 67 marauding orcs to ignore the PCs. City dwellers, though? They can ignore anything. They have to.