While chatting with a friend about meeting up in eastern Tokyo, I typed in ひがしとうきょう and my Mac dutifully sent 東東京 out the wire. I quickly clarified with ひがし東京 just so she wouldn't think I had made a weird typo or something.
But is 東東京 actually the correct way to write "eastern Tokyo," or is there a less ambiguous way to do so? Is there a uniform way to refer to directions inside of place names which feature directional kanji - could the same rule apply to "northern Hokkaido" and so on?
These should work:
道〜 (something) if the context is fairly clear that one is talking about Hokkaido.
For example: 道産子{どさんこ} (someone who grew up in Hokkaido.)
While 東東京 is correct and is used relatively often....
In most cases you are better off the state the exact area you wish to talk about.
Remember Japanese people think in terms of Prefecture - City - Station - etc. If you start talking too geographically you are likely to confuse them.
Many Japanese exchange students in my city say they are confused when people use absolute directions, despite the fact there is a huge land mark to the south.
So I would say use 東東京 if absolutely needed, but avoid it whenever possible.
