In Apple’s [video overview][1] of the new iPhone’s softscreen keyboard, the company revealed an interesting feature: by using predictive text algorithms, the phone not only offers suggestions for the words you type, but it also subtly changes each key’s clickable area based on the letters it anticipates you’ll click next. For example, if you’re spelling the word _time_ and begin typing _T-I-M…_, the iPhone checks its dictionary for possible words you might intend to type, and it enlarges the clickable area of the letter likely to occur next (in this case the letter _E)_ even letting _E’s_ target area encroach into the surrounding letters on the keyboard (_W_ and _R)_, if those keys aren’t part of the word.

Not only is this feature a savvy way to make typing on the slick, on-screen keyboard a little easier, it’s an excellent application of [Fitt’s law][2].

[1]: http://www.apple.com/iphone/usingiphone/keyboard_large.html “Apple’s video overview of the new iPhone keyboard”
[2]: http://en.wikipedia.org/wiki/Fitts%27_law “Fitts’ Law on Wikipedia”

According to the book [Universal Principles of Design][3], Fitt’s Law states:

> The time required to move to a target is a function of the target size and the distance to the target.

That is, with regards to a user interface, it’s easier to reach a target if it’s BIG or if it’s close…or if it’s both big and close. With the iPhone keyboard, Apple’s effectively making the keys bigger as the phone guesses what you’re typing, and thus it’s making the phones UI easier to handle.

Apple has toyed around with Fitts’ law in the past, too. In OS X, the dock grows and shrinks as you mouse over icons if you’ve got magnification turned on. There, both the distance to _and_ the size of the icons changes as you approach them.

Also in OS X, the Apple menu and Spotlight buttons in the top left and right corners of the screen cannily appropriate the Fitts’ doctrine to make the smallish-looking buttons easier to click. Since these buttons are situated at the screen corners, the user can move the mouse cursor as far up and off the side of the screen as they want; they don’t have to zero in on the buttons because the cursor is trapped in the screen, and it will end up on the intended button with even the most hamfisted push in the right direction. Effectively, these buttons each extend infinitely in two directions, the directions off-screen.

I’m still not sure how well the iPhone’s keyboard will work, but I was blown away to see how much thought Apple has given to making the tricky on-screen keyboard a good alternative to a clicky, hardware keyboard.

[3]: http://www.amazon.com/Universal-Principles-Design-Usability-Perception/dp/1592530079/ref=sr_1_1/104-9151830-2928739?ie=UTF8&s=books&qid=1182986093&sr=8-1 “Universal Principles of Design on Amazon”