NZ ranks 76 in list of countries by size, but only about 120 or 125 (United Nations) by population.
Say x in 1000 footballers is top class, 2x are next level, 5x next level below etc, expected ranking can be extrapolated.
Lots of other variables of course; history of football in country, whether football is tier 1, 2 or 3 sport (eg, India has never been big on football and more into cricket, so not expected to be top despite one of largest populations). And some nations don't play much or don't have the infrastructure. We are Rugby dominant, Uruguay football dominant, so they are likely to do better despite a slightly smaller population. PNG have twice our population but likely to be lower due to their history/environment etc.
FIFA rankings are up and down a lot depending on what games you've been playing - and IF you've been playing. E.g. When we do a bunch of qualifiers against PI nations and win them all we shot up 30, 40, 50 places. When we don,t play much we slide down.
Pick a number between 80 and 120, and anything above that we are punching above out weight. I would put that number around the 80-100 range.
Interestingly our ELO rating http://www.eloratings.net/ has us at 83. ELO rating gives a much longer term and less volatile view.
Gave you a 'This' for bringing up ELO. This is what we should be using to rank ourselves definitely as it's far more accurate, though there are a few strange placements (Algeria 80, Northern Cyprus 92, Oman 71)