In a great post called Always On, Adam Lisagor wrote about a subtle feature of the built-in iPhone camera app that makes your photos less blurry. It was a perfect I-see-what-you-did-there: a rare example of designers and engineers refusing to take the easy way out when clearly they could have gotten away with it. In the same spirit, I decided to write about something that impressed me in the desktop Mac OS. This might be old news, but I just noticed it.
You know how it’s easier to click on things that are at the edges of the screen, because you don’t have to aim as precisely? Well, that’s because of something called Fitts’s Law, which is fancy-talk for the fact that the bigger a target is, the easier it is to “acquire” with the mouse. Specifically, what matters most is the size of the object along the axis of motion of the mouse, which means the edges and corners can be considered infinitely large because you can’t overshoot them. So the best places to put a commonly clicked user interface element are at the edge of the screen (which is infinite along either the horizontal or the vertical axis) and in the corner (infinite along both axes). Acquiring a corner or an edge takes no time or thought at all; you just heave the mouse in that general direction until it stops.
Apple knew this when they decided to a) put the Apple menu in the upper-left corner and b) make its clickable area extend all the way leftwards (see below), so you could activate it just by slinging the mouse vaguely up and to the left.1
The same ease-of-acquisition applies to the Spotlight menu, which is in the upper-right corner. And, of course, Mac OS X’s menus are glued to the top of the screen, so for purposes of Fitts’s law, the entire menu bar is infinitely tall.
But what happens when you have two monitors arranged side by side, so what used to be corners are now just ordinary points along a horizontal edge of one big desktop? The menu bar can’t span two screens, so whichever end is on the inside loses that Fitts magic and becomes much harder to click, right?
Nope. Apple’s engineers are smarter than that. If the OS detects that your pointer is approaching one of those “internal corners” at a steep enough angle and with sufficient velocity, it pretends the other screen doesn’t exist for a moment and stops you right where you want.
To me, this is perfect user interface design. It anticipates your expectation and silently arranges things so that you aren’t surprised — most likely, you don’t even notice anything funny is going on. And in every other case where you’re moving the mouse near a false corner, it leaves you alone to do as you please.
This isn’t a feature Apple advertises — it’s not even a user preference because it’s completely unobtrusive, and probably 99% of users will never encounter it because they stick with a single screen — but if you need it, it’s there, quietly making your life a tiny bit easier.
1In contrast, Microsoft seemed to have heard a rumor that corners were useful when it decided where to put the Start button in Windows 95, but since the button itself was inset by one pixel, you couldn’t actually click it by aiming for the corner. (They finally fixed this blunder six years later, in Windows XP.)