Was this a deliberate act of design? How come there are so few cities?
As Renshai and Jeff LaSala have mentioned, space considerations were doubtless the reason that so few cities and towns were described. And too, hamlets and vilages mentioned were generally either notable or typical for the region.
With Known Realms, I'm going with a classic 1 in 10 rule of thumb for urban population, i.e., 1 in 10 people in a medieval state, on average, will be found in a town, city, or metropolis (1 in 20 for nomadic, barbaric, or similar peoples). Thus, we have the known cities of Crieste, with a population of 3,209,000, a potential urban population of 320,900 and a current total listed urban population of 189,937, broken down thusly in descending order of population:
Kassantia (Large Metropolis, 62,870)
Archbridge (Large Metropolis, 48,250)
Tarrasine (Large City, 24,021)
Blihai (Large City, 16,801)
Sirael Citadel (Small City, 11,901)
Vernaut (Small City, 11,680)
Vaquerea (Small City, 8,110)
Dhavosin (Large Town, 4,014)
Sparport Watch (Small Town, 1,380)
High Cross (Small Town, 910)
Total assigned urban population: 189,937. Total urban population yet to be assigned: 130,969.
A couple of notes on creating new cities and towns:
Generally, create new cities and towns at a distance from existing cities and towns. Don't drop another city just 20 miles away from Archbridge without a good reason. Cities exist for a good reason, and usually they use up that good reason for a good space around.
Unless you go against the design as presented (which of course, anyone is free to do), the largest city you can put in the Northlands would be around 60,000, as Punjar is described as the largest city in the Northlands at 75,100, and Kassantia the second-largest at 62,870. Kassantia is also the most "eldritch" (i.e., openly arcane) while Arvale is the most "divinely inspired." Morazuin is the most grossly evil and huge (illogically and impossibly so, due to its nature), and so forth. These will be benchmarks against which to measure your cities and towns.
Remember, too, that some states like Freeport, Porthmeor, and Wildsgate are no more than cities, and thus include a totally urban popultion in their description. As long as they have the trade ability to do that, such isolated cities can exist, but in general, a city needs a rural population about 10 times its own to support it.