Scale is not an issue, because Quartz and UIKit now work in 'points' rather than in pixels, so that's already accounted for. However orientation is not, [UIScreen mainScreen] will return the same rect either for applicationFrame or bounds etc, it's oblivious to orientation.
I like to put a solution in a category on UIView or UIViewController, because you'll reuse it plenty. something like this...
-(CGRect )workingCanvas{
CGRect screenRect = [UIScreen mainScreen].bounds;
BOOL landscape = UIInterfaceOrientationIsLandscape([[UIApplication sharedApplication] statusBarOrientation]);
CGRect result = CGRectZero;
CGFloat lesserDimension = (screenRect.size.width < screenRect.size.height) ? screenRect.size.width : screenRect.size.height;
CGFloat greaterDimension = (screenRect.size.width > screenRect.size.height) ? screenRect.size.width : screenRect.size.height;
result.size.width = (landscape) ? greaterDimension : lesserDimension;
result.size.height = (landscape) ? lesserDimension : greaterDimension;
if ([[UIApplication sharedApplication]isStatusBarVisible]){
result.size.height -= [[UIApplication sharedApplication]statusBarFrame].size.height;
}
return result;
}