I chose Britain as the outline for my map.
There was an interesting, historical reason for doing so. Omu was inspired by I1: Dwellers of the Forbidden City, which was memorable to me for its isometric city map. I'm a big fan of pictorial maps, and I loved the idea of presenting players with a handout map of the city when they arrived on the scene.
In researching Dwellers, I found a thread that suggested the original map's outline was based on the state of Alaska. I don't actually think it was, but as a Brit, I thought it would be fun to do something similar for Omu. For the outline, I just flipped Britain on its side. This provided an organic shape for me to trace in SketchUp, which is my preferred program for blocking out city maps. With the outline in place, I extruded some buildings in 3D to sculpt the basic shape of the city.
Initially, I thought I'd differentiate Omu from Dwellers by placing it atop a high jungle plateau surrounded by sheer cliffs. Chris wasn't keen on the idea though, so we stuck with the ravine layout. His brief for designing Omu was very flexible: it needed to have nine trickster god shrines, and the Fane of the Night Serpent underneath. The Tomb of the Nine Gods was originally supposed to be under the fane, but I thought it was more compelling to place the entrance within the city itself (primarily so I could present an Indiana Jones-style race for the puzzle stones against the nazis *ahem* red wizards).
TRPG cartography is a tricky mix of design considerations: gameplay, visual aesthetics, clarity on the page, and an interesting theme. For Omu, I wanted the city to look exotic and full of adventure. I flooded a large part of the settlement (as per the original Dwellers), and then collapsed a section into a lava-filled rift. I loved the idea of steam coiling up from where the water plunges into the lava, cloaking the city in hot mist. I also had an idea that the lower levels of the tomb would be a bit like Temple of Doom.
Replicating the rival factions of Dwellers was very important to me: it's what made that adventure so open-ended. I added a ruined market for my shrine-repairing kobolds, placed some grungs in the swampy section, created a palace district for the yuan-ti, and put the red wizard camp near the entrance so players could encounter that faction early. The "King of Feathers" was a nod to one of my one-page dungeons: Island of the Lizard God, which was set on an Isle of Dread-styled island and featured a roaming, godzilla-sized T-Rex (I was also keen for Chris to include a feathered dinosaur to represent current thinking on these species).
One of the first things I settled on were the raised boulevards. I wanted something that would provide quick travel through the city, but also expose you to its monstrous inhabitants: a classic, risk/reward choice. Thinking about how to navigate the city also gave me the idea for Bag of Nails: a crazed tabaxi hunter who came to Omu to die in combat with the most fearsome beasts he could find. His predicament (and his final treachery) were somewhat inspired by Laurence Fishburn's character in Predators.
While I was working on these features, Chris requested that I flip the map to portrait layout. This distanced the map from Dwellers, but made better sense for layout. I exported my map in wireframe from SketchUp, printed it out in blue ink (so it could be erased later in Photoshop), and began the process of fleshing out the final draft in pencil and black fineliner. Here's what I ended up with:
This final version was then passed to the cartographer, Mike Schley. I've had a few of my D&D maps worked up by Mike (my first ever Dungeon mag adventure had his expert hand all over it). He's one of the best RPG cartographers out there, so it was an honour to have him tackle the maps I drew for Chult. Best of all, studying his work led to many improvements in my own, as I could see first-hand how he modified my drawings to improve them. This was his final version of Omu!
Drawing Omu also inspired me to tackle Chult's original lost city, Mezro. Using similar techniques, Stacey and I created the following map for my Ruins of Mezro Guild Adept supplement. I think it's one of the best maps we've ever made!
I couldn't end this without sharing the amazing model version that Mat Smith (aka czarofhappiness) made for the live game set in Omu. When I saw this for the first time, I almost fell over:
Until then, Merry Christmas!