Urban Adventuring in Ravnica

Your classic, typical D&D campaign will, at least to begin with, generally involve small villages and travel through wilderness. Cities are certainly an element in D&D, but usually they're relatively safe places where you might need to watch your behavior so as not to be arrested by the city guard. Danger in cities tends to be exceptional, rather that the expectation you have when crossing a dangerous wilderness.

Ravnica is a purely urban setting - you can't leave the city without leaving the plane.

Now, to be certain, there are equivalents to the "wilderness." Expanses of ruins like the Rubble Belt can function quite a bit like non-Urban environments, only that rather than remote villages you'll find various members of the Gruul Clans. Ravnica's Undercity is more or less its equivalent to the Underdark, and given that the vast majority of Ravnica's populace really prefers to be able to see the sky, its inhabitants are going to be stranger - you might be forced to call upon the hospitality of the Golgari to avoid getting eaten by horrible monsters and... well, zombies that are part of the Golgari.

So you can avoid the crowded bustle of the city if you want when planning Ravnica adventures, but I think the fun of the setting is to lean into that urban density.

Let's say your party has been assigned to go track down some serial killer. You've discovered that they have ties to the Cult of Rakdos, and so a group of motley-costumed thugs come to attack you on the streets.

When putting together the encounter, the DM should account for not just the party and the enemies, but also put a bunch of civilians in harm's way, as well as environmental effects that might cause problems or be exploitable, like a nearby aqueduct or a cart full of small round fruits that, if spilled, could make the ground around it difficult terrain. This gives your players the a chance to figure out their values on the spot - your Boros Paladin might eagerly charge in and put herself between the thugs and that crippled street vendor who is trying to hobble away on his cane. Your Izzet Sorcerer might blast them with a fireball and then immediately regret it as the scaffolding on the nearby building is engulfed. Your Orzhov Cleric might not give a crap about what happens to innocent bystanders and drops a Flame Strike on the enemies and anyone near them.

Another potentially interesting element in Ravnica is that it's likely the party has homes. People joke about D&D parties often tending to be kind of Murder Hobos - simply moving from place to place and picking up loot as they go. But in a place like Ravnica, it makes sense that your players would have an apartment to go back to. The plane is just as big as any world, but it's also a city that has established routes of transportation. Giving each character neighbors and acquaintances outside of the party can really help flesh out the RP element of the game.

Guilds obviously provide a structure here as well. In other settings, players can belong to certain factions, but in Ravnica, these groups are built into the very structure of the setting. Yes, you can play a guildless character (though I think as DM I'd not allow that for at least peoples' first characters) but putting each person in a guild gives them not only obvious connections to NPCs, but also gives you a whole class of NPC that would have certain behaviors associated with them.

This means that players are not necessarily as anonymous as they would be in other settings - yes, Ravnica's got to have like trillions of people in it if the plane is anywhere near as big as Earth, but it's all settled and all more or less under one unified system - the Guildpact - which means that there are going to be people who know who you are.