If you're an iOS7 user, you've noticed something very different from the previous look and feel of iOS: gone are the icons and apps that looked like their "real-world" counterparts. The Notes app no longer looks like a pad of paper; Newsstand doesn't simulate wood shelves on which to "hold" virtual books; Game Center ditched the green felt of casino gaming tables. Skeuomorphism is out, and flatness is in. (See Apple's redesigned icons here, and many more examples here.)

"Flatness" isn't just something that is now part of iOS7's aesthetics. Flatness can also be thought of as the reduction or elimination of affordances. And this directly affects usability, which is why I (as a user experience designer) am interested in it.

What's an affordance?

An affordance is "a property of an object...which allows an individual to perform an action." In the real world, a good doorknob says "Twist me!" In the world of computer and phone applications, buttons and labels have traditionally broadcast to us how to interact with the screen. But as iOS has grown up, some of those affordances have been removed, and the interaction design has been flattened.

Above (left) is the Reminder app from iOS6; it's pretty clear that tapping the + icon is the way to enter a new reminder. On the right is what Reminders looks like in iOS7; where would you tap to add a reminder? (HINT: "Edit" isn't what you're looking for.)