Sheeesh!  Nerima doesn't really exist.  If you want it under 30 km from
the
Imperial Palace, it's under
30 km.  Heck, you could put it right next to the palace if you wanted to.
<<<<<<<<<<<<<<<

Someone hasn't been paying attention...

Actually, Nerima does exist.  It is a ward in the northwestern part of
Tokyo (just past Ikebukuro).  In fact, I have been there.  It is actually quite
large, but also unexciting and rather nondescript (for Japan).  I suspect
these features are what impelled RT to choose it as the site for Ranma.