Screen and interface
The 9 cm liquid crystal display (320×480 px at 6.3 px/mm, 160 ppi) HVGA touchscreen with scratch-resistant glass is specifically created for use with a finger, or multiple fingers for multi-touch sensing. Because the screen is a capacitive touchscreen, bare skin is required whenever a style or a normal glove prevents the necessary electrical conductivity.
Almost all input is given through the touch screen, which understands complex gestures using multi-touch. The iPhone user interface enables the user to move the content itself up or down by a touch-drag motion of the finger. For example, zooming in and out of web pages and photos is done by placing two fingers on the screen and spreading them farther apart or closer together. Similarly, scrolling through a long list in a menu works as if the list is pasted on the outer surface of a wheel: the wheel can be "spun" by sliding a finger over the display from bottom to top (or vice versa). In either case, the list continues to move based on the flicking motion of the finger, slowly decelerating as if affected by friction. In this way, the interface simulates the physics of a real 3D object. There are other visual effects, such as horizontally sliding sub-selections and co-selections from right and left, vertically sliding system menus from the bottom (e.g. favorites, keyboard), and menus and widgets that turn around to allow settings to be configured on their back sides.
The display responds to three sensors. A proximity sensor shuts off the display and touchscreen when the iPhone is brought near the face to save battery power and to prevent inadvertent inputs from the user's face and ears. An ambient light sensor adjusts the display brightness which in turn saves battery power. A 3-axis accelerometer senses the orientation of the phone and changes the screen accordingly. Photo browsing, web browsing, and music playing support both upright and left or right widescreen orientations, while videos play in only one widescreen orientation.
A software update allowed the first generation iPhone to use cell towers and Wi-Fi networks to locate itself despite lacking a hardware GPS. The iPhone 3G includes A-GPS but also uses cell towers and Wi-Fi for location finding.
A single "home" hardware button below the display brings up the main menu. Subselections are made via the touchscreen. The iPhone utilizes a full-paged display, with context-specific submenus at the top and/or bottom of each page, sometimes depending on screen orientation. Detail pages display the equivalent of a "Back" button to return to the parent menu.
