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?

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

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You could let them select their own paper size.