Though it was shown sparingly at E3, we weren't sure what this new method of control would look like. Thanks to the new image we now have at least a slightly better idea.
Seen below, the image shows the player manipulating the game with what looks like an iPad. The tablet shows an isometric view of the city from above. According to a Destructoid (opens in new tab) interview, the Watch Dogs app functions as something of a companion to the main game rather than a standalone experience.
The app is essentially a map which allows you to better keep tabs on your game. For instance, we're told that once you've hacked somebody in-game, you'll be able to monitor their position at all times via the companion app. You can also use the app to monitor what your friends are doing in the game, and even affect their world (if they give you permission.)