There are many reputable studies which have measured penis length. Pleaseeeee don't trust those "world penis map" or "self-measured length" as they are highly inaccurate. In general, most men regardless of ethnicity, fall within the same average range. I highly recommend researching some studies conducted by universities, hospitals and military.
However, from my own personal encounters with men, I did find African men did tend to have a big size. The South American men I've met were mostly average in length and some were small. I would have to say I met more Asian guys with big ones but this is just my own personal experience and of course, penis length doesn't mean anything to me.