To be honest, both questions can be answered in a few seconds by looking at the code point table for Hiragana/Katakana if you already know Japanese. Hence, that's why nobody write about it.
> How do the 46 characters map into the 90 characters?
Because there are actually more than 46 characters.
> Do they map the same way for both hiragana and katakana?
Yes. That's also how we do conversion between hiragana and katakana. By adding/subtracting 0x60.
> How do the 46 characters map into the 90 characters?
Because there are actually more than 46 characters.
> Do they map the same way for both hiragana and katakana?
Yes. That's also how we do conversion between hiragana and katakana. By adding/subtracting 0x60.