Ravnica is special in that no single map can encompass the tremendous scope of its sprawl, and its borders (if it has any) are unknown.
Most adventures that take place in Ravnica focus on its core, sometimes known as the City Proper, that is divided into 10 Districts, each of which is a huge urban environment all its own.
The Tenth District, in particular, is a hotbed of activity where all of the Guilds maintain their primary headquarters, the Guildhalls. The most important recent events that have taken place did so in this famous district, including the infamous Decamillennial that shattered the Guildpact.
The Tenth District is divided into Six Precincts by the various Guilds who have vested interests in different parts of the town. This grouping results in each Precinct having different economic classes yet living right next to one another. As such, some of these neighborhoods are safer than others, even in the city's capital.