Whatever floats your boat - I suppose.
I agree that being in Tokyo, you`re going to have a lot to count. Most foreigners in Japan never leave Tokyo - and those who do tend mostly just take a trip to Kyoto.
I can`t say that I find the idea of going about counting foreigners a fun one - but just to offer my "Not in Tokyo" view, I`ll join in. (And because I know that as I am not in Tokyo or Kyoto, it will be incredibly easy for me.
)
I spent my entire day out and about today as the weather was wonderfully and amazingly nice and cool. I saw one (1) possible foreigner. A woman who looked very Southeast Asian all the way to her clothes and hairstyle. :P