The Assassin's Creed Mirage map is roughly the same size as Revelations' Constantinople

gamesradar.com:

Assassin's Creed Mirage's map is roughly the same size as Revelations' Constantinople, according to Ubisoft. 

A lot has changed in the Assassin's Creed series since it debuted in 2007, particularly with its most recent instalments, which swapped stealth gameplay for a more combat-heavy experience in sprawling locations. The newest entry, Assassin's Creed Mirage, is set to change all that and return the series to its roots with a scaled-back, stealth-focused adventure that's much more reminiscent of the original. Now Ubisoft has given us a better idea of the size of the area we'll be sneaking and leaping our way around in the upcoming game. 

As reported by MP1st, Ubisoft, speaking to Easy Allies at Summer Game Fest, revealed that the map in Assassin's Creed Mirage is similar in size to two earlier Assassin's Creed games. "They compared it specifically to Constantinople in Assassin's Creed Revelations and Paris in Assassin's Creed Unity," explained Easy Allies' Michael Huber. "They said it's about that big."

According to this comparison video, Constantinople in Revelations is 0.94 km2 in size, while Paris in Unity is 2.40 km2, so we'd expect Mirage to be somewhere between the two.

If you've played either of these games, you'll know that they offer sizeable yet manageable playgrounds, but they are significantly smaller than the mammoth maps in the series latest entries. According to the same video, Valhalla's England is 94 km2,  while Greece in Odyssey is a whopping 130 km2. Also, if you're wondering how Mirage compares to the earliest game, Damascus from the original Assassin's Creed is said to be 0.13 km2. 

Far from seeing it as a negative, this smaller scope is what many Assassin's Creed fans exhausted with enormous RPGs