The debate as to whether fragmentation is becoming a problem on iOS is raging on, but I will certainly admit that I find it difficult to keep track of all the different screen resolutions. Thankfully, the people behind PaintCode have created a very handy guide that makes it a lot easier. The guide covers every device from the original iPhone to the new iPhone 6 Plus detailing points in coordinate space, rendered pixel resolutions, downsampling/upsampling scales and physical device sizes with pixel density. They've even included details of Display Zoom on the iPhone 6 and 6 Plus.