He is explaining that if you design an app that displays as desired on the outer display (in portrait mode). Then if you display that app to the inner display (also in portrait mode), it will show up exactly the same, just with everything twice as large.
This obviously makes life easier for both users and developers.
Size is even more important for UI design. If you don't think you need to re-design the layout of your app when the screen doubles in size, you shouldn't be doing UI design.
Moreover, app developers for iOS have to support fewer aspect ratios than developers of Android apps. In theory, this allows for more attention to be given to the UI design for each aspect ratio - rather than having to use a spring-style stretch layout.
If I were to guess, this does look like a new ratio to support, but at least it's just 1 instead of 2.
But why paper's ratio is important?
He is explaining that if you design an app that displays as desired on the outer display (in portrait mode). Then if you display that app to the inner display (also in portrait mode), it will show up exactly the same, just with everything twice as large.
This obviously makes life easier for both users and developers.
It's mathematically the only aspect ratio where this holds and thus you can resize in half and nothing has to move around.
One reason is making it easy to scale things up or down for printing on standard sizes of paper.
Size is even more important for UI design. If you don't think you need to re-design the layout of your app when the screen doubles in size, you shouldn't be doing UI design.
Moreover, app developers for iOS have to support fewer aspect ratios than developers of Android apps. In theory, this allows for more attention to be given to the UI design for each aspect ratio - rather than having to use a spring-style stretch layout.
If I were to guess, this does look like a new ratio to support, but at least it's just 1 instead of 2.