Istanbul is the modern-day name for the city represented by Constantinople in Assassin's Creed: Revelations.
The game takes place mainly in Constantinople during the early sixteenth century, when Ezio travels there in pursuit of Altaïr's legacy and a set of ancient Masyaf keys. The city is divided into districts and includes locations based on the historic Byzantine and Ottoman capital.
Constantinople was the name widely used for the city in the game's period. The name Istanbul became standard internationally over later centuries and is the name used for the modern Turkish metropolis. Thus, Istanbul and Constantinople refer to the same urban location, but they reflect different historical naming contexts.
Revelations also includes Cappadocia and a playable version of Masyaf. Its historical story links Ezio with Altaïr, the protagonist of the first game, while the modern-day sections continue the storyline of Desmond Miles. The setting therefore connects multiple generations of the series.