Google maps uses bmp image tiles, whereas ios maps uses vectors. The maps will be the same, but they can be displayed differently.
In Google you are zooming in and out of an image, like moving a piece of paper closer/further away from your face. Whereas vectors are based on mathematical expression, so when you zoom in the computer makes a calculation (this line was in position x and of thickness y when zoom was z%, increased zoom by a% means position b thickness c).
Vectors also mean you can hide certain parts of the map if you wish to reduce clutter, as you see a narrow street dead end is hidden because the name "Pleasance Theatre Box Office" is written over it's position. As you zoom in the dead end would come into view as the Box Office moves out of view.
Same with building outlines, if you were to zoom in closer on ios the buildings would come into view.
The perfect map right now would be iOS vector and google data, but that's not going to happen so both companies are going to race to implement each others tech over the next few years.