Last time I argued that there would be more forestborn than cityborn these figures were used:
And this is referring to a single city for an area equalling 2/3rds the size of Nordland.
You know how Warhammer has abysmal population figures? Last time I posted about it, Boney gave me a rough multiplication figure of x100 to get the actual population. That was an offhand mention, but he did say that at the current time period hundreds of thousands of people can in fact live in a city if it's big enough. So, I'm going to give you the canon population figures of the four most major Warhammer cities, then to make them more realistic, because we know Warhammer sucks at population figures, I'll multiply them by 10. Not 100, because the figures would be absurd otherwise:
Nuln: 120,000/1.2 million
Altdorf: 105,000/1.05 million
Middenheim: 95,000/ 950k
Talabheim: 72,000/ 720k
I should mention that in canon, the average village has around 50 or less people. A large town has around a 1000. A city has 10,000.
If we take the modified values of only the four most major cities of the Empire, and then compare them to the rough 15mil figure, you find that those four cities account for 3.92million.
Roughly 38% of the Empire's population lives in only four cities. I don't know about you, but that figure makes sense to me. Now if you include every urban population center in the Empire, accounting for cities and towns (which are urban), your figure would almost certainly come about to see that the majority of the Empire's population is in fact urban.