One of Mafia II's drawbacks was the extremely long driving times often required by a map that spread mission points very far apart. L.A. Noire will be twice the size - 20sqkm to Empire Bay's four - and will require 30 minutes to traverse by car.
So let's hope they place the mission locations closer together, or you're going to understand the joy of L.A. traffic before there were freeways. A Rockstar developer confirmed the map size a couple months ago in a Rockstar forum; but with the game's addition to the Social Club community this week, the general public got a small look at the City of Angels' big map. It is bigger than Grand Theft Auto IV's, which was six square miles.
There are five other screenshots at the Social Club, an offer of free DLC (a suit for goin' shotgunnin' in) if you sign up, and a full explanation of benefits you get if you play the game through your account. Signing up for that is free.