3.5 inches ? Not so fast.
In his blog, Dustin Curtis explained why Apple continues with 3.5 inch iPhones while Android and Windows phones all have larger screens.
His discovery: because one-handed use of 3.5 inch phone allows user to “touch any area of the screen while holding the phone in one hand, with your thumb.”
I totally agree with him that all these large screen Android phones are difficult to use single-handedly. But I would like to uncover a hidden assumption in such a view, which I believe is also the view of Apple’s (or rather, Steve Jobs’). Maybe by doing this will point us to a new kind of mobile OS, or UI design.
The point of a touchscreen is that it is not just a display (visual output) interface, but also an input (touch input) interface. Purely from the visual perspective, user will want a screen as large as possible, so that more information can be displayed without being cramped.
Now, it seems to be the common view (and Dustin’s view) that a larger screen means it is more difficult to operate single-handedly, in general. This sounds reasonable - holding the phone with one hand and try to reach an icon on the opposite side of the screen using your thumb is not possible without awkwardly adjusting your hand position (for 5” and above it seems downright impossible, or extremely difficult).
However, there is a hidden assumption to this view:
Why make the UI such that your finger need to be at the location of an icon in order to touch it?
One can, for example, create a small half-opaque area (which can be a semicircle shape) that can pop in and out from the edge of the screen, which serves as a “virtual trackpad” for the entire screen. When the thumb moves around the “trackpad”, there is a small highlighted circle moving correspondingly around the entire screen of the device. Tapping your thumb twice at a certain location of the “trackpad” means pressing the corresponding location of the touchscreen.
This allows the entire screen to be accessible by your thumb while holding the device single-handedly.
I can also imagine the default function of this trackpad to be customizable according to when it is being activated, so that it has other advantages such as:
1. When activating this trackpad inside a web browser, a list of miniaturised tab thumbnails appeared around the edge of the trackpad so that user can go to (and close) any tabs quickly. So now the tab list on top of the screen is unnecessary, and we can always surf webpages at full screen mode.
2. In general, activating this trackpad in any app also brings out a list of running apps, so that user can easily open (and close) any running apps.
3. Activating the trackpad in pictures will call up an analog zoom icon, so that by using one thumb we can easily zoom in and out.
I would like to add that this “virtual trackpad” is purely optional, so that anyone can use their phone with OR without it, by turning it on or off. The location of the “trackpad” is also movable, along the edge of the screen, or on both right and left sides of the screen.
Whether a device is usable by one hand not only depends on its size, but also on its UI (or OS). As another example, Windows’ metro-like tiles are more usable single-handedly than android because of its large tiles, and that its text-like icons are arranged in rows.
(Of course, portability will also matter if a screen size gets too large. But my discussion here targets at devices from 4” to 5+”, which are still pocketable)