Since the iPhone and iPad come in different screen sizes, every iOS app needs to adapt to these different screen sizes depending on the type of iOS device it’s running on. To define the position and spacing of different user interface objects, you can use constraints.
Constraints can define the following:
Position (such as the center of the screen)
Size (such as the width or height of an object)
Distance (such as the space between two objects)
Without constraints, objects on the user interface might look good on one size iOS screen but look completely skewered on another ...
