Japans smallest town/city radius?

[ArgentDragonPluto]

So let's say characters find a small town that has been abandoned. Is it possible to use the radius of Japans smallest town/city for this fictional town as a low end and then have feats calculated based on the size? Mostly asking because it's in a LN and I can't think of a better way to find the size. And if possible can someone find the size of Japans smallest town/city? I've looked but can't get a good answer.

 

[GoldExPoints]

Kind of a necro, but the smallest city in Japan is Warabi, Saitama which is 5.11 km^2 in area. It doesn't really have a radius, since it's more rectangular in shape tho