Designing for iOS

When creating an app for iOS, you need to know about the platform you are working with, how it can work best on the platform, and the technical limitations of it. With the iPad and iOS, there are certain guidelines that must be adhered to when designing for it.

"Retina - Most recent iPhones and iPads are fitted with Retina screens, a high resolution screen intended to make pixels invisible. The Retina resolution of a device is an exact doubling of the previous resolution. A single pixel in a non-retina iOS device is taken up by four pixels in the retina version. This makes text crisper and allows for significantly more subtle detail. There are many complexities to designing for retina screens, so this is an important area to read up on."

"Pixels - A pixel (px) is the smallest unit of measurement on a screen. It represents a minuscule physical square that is part of the display. If you look very closely at a screen, you'll be able to see them (and the gaps between).

It is not possible to have a line that is smaller than "1px" in width. For example a 0.4px line can't possibly exist, instead graphics software interprets this as a fainter 1px line. This result is often considered ugly."

"Points - We use points (pt) as a resolution independent measure. A point can be represented by many pixels, normally one or two in a single dimension (high or wide). For example all iPads have the same resolution in points and all iPhones have the same width in points.

Over time you'll learn to think in points rather than pixels. But it's important to remember that each point can be made of many pixels and so there is room for extra detail."
http://taybenlor.com/2013/05/21/designing-for-ios.html

These are various things that should be kept in mind while designing for iOS. Retina screens are not in all iOS products, so users of both should be considered when designing for iOS.

Device	Retina?	Point Resolution (pt)	Pixel Resolution (px)
iPhone < 3GS		320 x 480	320 x 480
iPhone 4, 4S	eye	320 x 480	640 x 960
iPhone 5	eye	320 x 568	640 x 1136
iPad 1, 2 & Mini		768 x 1024	768 x 1024
iPad 3, 4	eye	768 x 1024	1536 x 2048