You know, that 'world penis size' map got a lot of press, in spite of the numbers being pulled out of the air. We don't have enough data to make such a comprehensive chart, but we can probably get a start on an accurate list that uses medical data. Posting reports by people who are attracted to big dicks and a certain ethnicity does not an accurate study make.
It's was demonstrated by the UERJ (the university in Rio) that maximally-stretched is really the only reproduceable and accurate methodology, as everything else leaves too many variables to chance (EQ, measurement bias, etc.) Chen et al. proved that stretched length is a reliable predictor of erect (Predicting penile size during erection. [Int J Impot Res. 2000] - PubMed - NCBI
). Makes sense, since your shaft won't get any longer than you can physically stretch it, though you may measure a little longer erect because your head will engorge too - you can add +1cm to account for this. Sample bias can be avoided by only posting where the group isn't selected based on their penises (eg conscripts, routine checkups.)
Based on these criteria, I know of:
Country - length - sample size - source
UK - 13cm - 103 - Can shoe size predict penile length? [BJU Int. 2002] - PubMed - NCBI
Nigeria - 13cm - 115 - Can physique and gluteal size predict... [West Afr J Med. 2006 Jul-Sep] - PubMed - NCBI
Iran - 11.58cm +/- 1.45cm - 1500 - Penile size and somatometric paramet... [Int J Impot Res. 2007 May-Jun] - PubMed - NCBI
Italy - 12.5cm - 3300 - Penile length and circumference: a study on 3,300 y... [Eur Urol. 2001] - PubMed - NCBI
US (California) - 12.4cm - 80 - Penile length in the flaccid and erect states: guidel... [J Urol. 1996] - PubMed - NCBI
Brasil - 14.5cm - 71 - Penile anthropometry in Brazilian ... [J Pediatr (Rio J). 2007 Sep-Oct] - PubMed - NCBI
Israel - 12.5cm - 55 - http://www.eng.tau.ac.il/~msbm/resou...12_328-333.pdf
I think brasil may bone-press, while the others don't, which explains the ~0.5" longer they register. BP + difference between stretched & erect is ~1.8cm, so I think ~15cm might be a more reasonable average to compare your (undoubtedly favourable) self-measurements against. Get as hard, or stretch as far as you want, jam that ruler in, and subtract from 15 to see how much above/below you are.
If you know of some more, please post them so I can compile as comprehensive a list as possible. Please don't post any garbage like the worldpenissize map, that just lists off a bunch of numbers but never actually says where they're from. Another site listed a world penis size map and claimed to cite reference materials, but after personally checking each and every one of the referenced pages, none actually reported the numbers they claimed.
So on my list, we have European, middle-eastern, Brasilian, sub-saharan African, and American. What should surprise many people (and I have no doubt that the majority will cling to their stereotypes in spite of a mountain of evidence to the contrary): nearly everywhere has the same average penis length. Could a certain population have a higher percentage of really big ones? If only 0.05% of guys are ~9" long, then a country with 0.15% 9"+ wouldn't really have a different average, but would have 3x as many 9"ers, so it's possible. This would, however, just be a guess. I don't think we really need to keep inventing explanations to keep the worldview we currently have.