@Hero\-of\-Time, @Tales Glad to see you both enjoying this game, the story itself was the seller for me. And playing this first over Unity is the best way, as you'll see for yourselves.
@somme, as Tales said the map is divided up into 3 sections. You get 2 ocean-bearing maps (Atlantic and River Valley) and New York being the 3rd. The Atlantic is the one filled with Ice bergs and snow, the Valley has some snow and ice up the Northern part.
Content-wise, there is a lot to collect and to do. Including Hunting, Fort + Hideout Liberations (across all maps). These are quite enjoyable i must say. As it's been said, think of this as a direct sequel to Black Flag.