How to Decide What Page Size to Use on an iOS Application

Wikipedia says that the US and 开发者_如何学运维Canada use letter size paper and the rest of the world uses A4 and that some countries use both. I want to create a PDF in my iPad application and am trying to figure out a clean way to determine whether to set my bounds to letter or A4. I am also looking for any common patterns used to let someone change from one size to the other.

I have already looked at this Stackoverflow question to get some of the basics down with region checking.

So, my question rephrased as a question: is there any way other than checking to see what region and then assuming that US/Canada are letter to know the user's preferred default paper size?

How about checking the user locale and decide based on that? See this question.

You could let them select their own paper size.