What shape is Los Angeles? I have no idea. (It's way bigger than The City-State of the Invincible Overlord, and that map is huge.)
I don't think anyone knows except maybe Noah Cross. Anyway, point is, I want the big cities in this campaign to be big and mysterious and noiry and, perhaps, in that way, unlike real medieval cities.
In the mind and in books and movies, the noir city is more like a dungeon than a mapped thing in a tour book--it's an amorphous dark space through which the characters grope and carve their way. It's a romantic rather than a classical approach to the city.
Plus, like I've said before, I don't want to world-build a lot of stuff I'll never use. So I'm writing some "urbancrawl" rules so that I can build the city as the PCs explore it.
Once a place is explored, it's fixed on the map. Until then, though, anything the DM hasn't written is up for grabs.
Above is a neighborhood map of Vornheim. It was achieved by writing out numbers one through ten in different colored markers. Pretty much randomly.
So far, as you can see, Vornheim has 10 neighborhoods, which is about a third as many as LA or Manhattan and about twice as many as Fritz Lieber appeared to need to write all the Lankhmar stories.
It doesn't show the actual shape of the city, just where neighborhoods are relative to each other and where the major streets and bridges are (Vornheim has building-to-building bridges everywhere--like Sharn in the Eberron setting and many previous pulp sci-fi cities, but for these rules, the bridges aren't necessary). For example, the fastest route from neighborhood ten to neighborhood four is via neighborhoods five or six, though you could go 10-9-2-1-4 if there was a giant lizard eating neighborhoods 5 and 6 or something.
Certain kinds of buildings there just isn't that many of even in a big medieval city. Like, Vornheim has:
2 Shipping operations (it's landlocked)
3 Major theaters
1 Spymaster's secret headquarters
2 (competing) Cathedrals
1 Independent library
4 Courts of law
If, in the middle of an adventure, the PCs suddenly need to know where one of these things is, or find some other unique place, roll a d10. That's what neighborhood it's in.
Getting From Neighborhood To Neighborhood
The major thoroughfares roughly match all the lines in the words spelling out the numbers in the neighborhood map. i.e. to get from neighborhood ten to neighborhood seven the PCs need to walk across a big "x" shaped intersection and if you flew in a dirigible over neighborhood six you'd see that the major streets spelled out the word "six".
(This is just the default street map for if a neighborhood is improvised during play. You always have the option of getting off your ass and mapping more realistic streets in any part of town, as long as the PCs haven't been through it yet. Plus if you count the bridges, there's several "layers" of connecting streets.)
Walking from one neighborhood to the next isn't that hard if the PCs know where they're going and it's daytime.
If it's not daytime, the DM may roll once on the Who Are You And Why Are You In My Way Table (Vornheim)(below)(Or any other random urban encounter table) once for each neighborhood the PCs travel through on their way to wherever they're going.
If they don't know where they're going, they can ask a random stranger for directions. Roll a charisma check. Success means they get where they're going. If they fail, the stranger isn't charmed enough to give conscientious directions, consult the following chart:
Fail by 1: You're lost, roll d10 to see what area you ended up in.
Fail by 2: You're in a dark alley, there's a thief trying to pick your pocket.
by 3: ...make that several thieves.
by 4: Refuses to give directions.
by 5: Refuses and is offended.
by 6: Person you're asking attacks you.
Some stuff is everywhere. Assume every neighborhood contains at least one of the kinds of buildings listed in the table below under "Random Individual Buildings". (This is probably unrealistic, like is there really a jeweller in every neighborhood? No. Is there only one? No. But in a pinch, it'll do.) This way if the PCs go--"We need the nearest cheesemaker, stat!" you just use the "Travel Within A Neighborhood" rules.
Travel Within A Neighborhood
Once the PCs are in the same neighborhood as whatever they're looking for, if the DM is lazy and hasn't mapped that neighborhood yet, s/he rolls a d10. The streets between the PC and his/her objective are shaped like whatever number comes up on the die. For example, if the PC comes into the neighborhood from the north and the DM rolls a "1" then the map to wherever the PC is going looks like this:
If it's in the middle of a pleasant and sunny day then the DM shows them this (and makes up some street names) and everyone goes, Well, gee, that's nice to know, the PCs note that down and the DM draws it onto the map of the neighborhood and that's that. (The streets aren't shaped like numbers--the segment of their journey that lies between them and their goal is. And often, it'll only be shaped like part of a number--in this case, the right half. Just add on extra side streets so they don't realize you're doing this.)
However, if the PCs run out of arrows durring a goblin invasion and desperately need arrows and want to find the nearest arrowsmith, then the DM doesn't show the PCs this little "1"-shaped map and watches them run around on it trying to find what they need.
If the PCs take a wrong turn and unwittingly run off the edge of the "1" into an unknown zone, simply roll d10 again for the layout of the streets they just ran onto.
Over time, once the PCs have been a few places in a neighborhood, the "known streets" of the neighborhood might look like this:
And the DM can flesh out the neighborhood at will and throw in "decoy" streets to disguise the scheme--it's easy, numbers are just straight lines and circles.
That's the same neighborhood after 5 seconds of extra streets.
All this is more complicated if you take into account the bridges, but for the sake of a single day's adventure this should do you. If a PC is on a bridge and gets knocked off to a lower "level" and doesn't climb back up, just start the process all over again on the lower city level.
Random Individual Buildings
If the PCs run into-, or just happen to be looking at-, a random building, roll d100 to determine what it is:
5-6-Alchemist (1-3 public apothecary, 4-6 private residence)
7-8-Weird shop full of random crap
9-10-Famous local eccentric's residence
11-12-Nest of criminals
15-16-Whatever the name is for someone who sells horses (ostler?)(stableman?)
26-27-Scholar (private residence)
57-58-General outfitter (expedition equipment)
63-65 Fortune Teller
78-100 Private residence
If a PC enters an unmapped bulding, roll d6. The layout of rooms on a given floor will roughly match the layout of dots on a standard casino d6, i.e.:
If it becomes relevant, roll 2d6 to determine number of floors (in Vornheim, anyway, for a more realistic city, roll a smaller die).
Each floor can be laid out the same or differently, depending on how frantic the pace of the game is.
(For major buildings, just roll more dice and put the layouts next to each other. Or just be slightly less of a slacker and have a few of those generic church/castle/great hall layouts printed out.)
Pubs, Inns, and Other Commercial Establishments
Have four short pub descriptions locked and loaded before any urbancrawl session. (i.e. "quietest pub in town, red curtains, drunk painter eating sausage at counter, pick-pocketable for 2d6 g.p., waitress is 9th-level anti-paladin, rooms are cheap"). If the PCs enter a pub or inn roll d4 to determine which one they walked into. If your PCs enter more than four pubs in one session then, well, God help you.
God or Jeff.
Once you use a pub, write a new one between sessions.
Likewise, write short descriptions for four generic local merchants, i.e. "takes forever, expensive, but has valuable information about last NPC party met" and do the same with them.
Random Schmuck Table
If the PCs accost someone and you want it to be interesting, roll on the Who Are You and Why Are You In My Way Table. If they accost somebody and you just want it to be some random loser, roll below or on the WFRP career table if you've got that:
28 Grain Merchant
47 Rat Catcher
61 Dwarf (roll again)
62 Elf (roll again)
63 Half-orc (roll again)
64 Tiefling (roll again)
65 Half-elf (roll again)
66 Roll on WAYAWAYIMW Table below
68 Extremely ugly child
69 Long lost relative (boring, but friendly and helpful)
70 Dog catcher
71 Thief (not working today)
75 Wife (non fish-)
76 Tavern wench
77 Strapping young lad, possibly unemployed
81 Confused foreigner of indeterminate occupation
82 Two goblins standing on top of each other hiding inside a human-shaped costume
84 Drunk noble
85 Creepy...(roll again)
86 One-legged...(roll again)
88 Bard (about to die of unknown causes) (authorities will be apathetic)
89 Tavern keeper
90 Fetch-it Boy
92 Siamese twin (roll twice)
93 Lovable scamp (1-3 red-headed 4-6 with stolen pie from windowsill) (is actually wererat)
94 Suspicious, evasive weirdo
95 Carnival freak
96 Fake carnival freak
97 PC chooses (holy shit it's all Gameforge in here!)
99 Doppleganger (roll again)(means no harm)
100 King/Local lord in disguise roaming amongst the common folk
Who Are You And Why Are You In My Way Table (Vornheim)
(empty spaces to be filled in by DM when PCs aren't looking)
2-Thugs (#=#of PCs)(level 1 fighters)(probably)
3-Kindly, helpful old woman, who happens to _______________
4-Fat fortune teller
5-Crazy poet who will __________
6-Drunk noble that __________
7-Drunk priest who ________ but only if ___________
9-Drunk commoner (1-3 funny 4-6 boring)
10-Aggressive Prostitute (roll on world's most famous AD&D DMG table)
11-Thief with intriguing proposition (possibly plot-relevant)
12-Creepy noble with intriguing proposition (possibly plot-relevant)
13-Dog, normal, except _____________
14-Frightened child being pursued by (roll again on this table)
15-Old man who is actually _______________
16-Disshevelled damsel in distress, being pursued by (roll again on this table)
17-Helpful NPC who ________
18-Street fight between goblin raiders and locals
20-Locked chest someone just threw out, containing _________
(Reader-suggested additions to this table welcome.)
Once an encounter has been used, cross it off and write a new one.
My "second string" so far includes...
-Travelling theatre (1-3 good 4-6 annoying)
-(Roll on table) being chased by (Roll on table)