I have always assumed that for an urban region (including the suburbs) the ratio between vampire and human population was about 1:10k and 1:50k for the biggest, capital cities. The rural region would yield a bigger ratio, about 1:5k-10k. I assumed that on the notion that in the scarcely populated regions vampires that would otherwise be scattered would group together, but in the largest centres the elders would thrive and gather more resources than their lesser peers.
However, I realised that I have never seen an actual passage from the book that describe this. Is there such a passage? Or maybe the vampire to human population ratio has been implied in one of the more obscure sourcebooks?
Also, if for some reason you believe my reasoning is wrong please let me know, though establishing correctness of my claim if there is no canon source is not an objective of this question.