Using my previous explanations, we have the following :
Depending on the terrain, each city region ranges from 500k-2 million acres. Basic rule is 50% of the land is arable (250k-1million acres), and 50% of the arable land is for foodstuffs (125k-500k acres). One third of the land has to lay fallow, which leaves us 84k-333k acres of staple foods.
Without magic augmentation, each farmer can work one acre and produce enough food for 3 people, giving us populations of 250k-1 million people. With magic augmenting the farming, 1.33 farmers can work each acre, each producing food for 3 people, giving us 336k-1.3 million total people.
Remember, that is at maximum saturation, with all land in production. Assuming you are at 50% max density and are halfway between the best and worst terrain, you have a "typical" region of around 400,000 people.
70% of the populace is rural, 30% urban, giving us a 280k/120k rural/urban distribution. Making a vague estimate that 15% of staples that would go to urban centers is used for trade or military supplies changes that to 280k/102k populations.
Out of the rural population, the majority are living in communities only two miles in diameter, with populations of 300 or less (Hamlets or Thorps) and the rest are in communities unlikely over 1000 (villages). I'd probably say about 60% are the smaller and 40% are the larger.
Rural population of 280,000
1120 Thorps (20% = 56,000 people @ 50people/thorpe )
466 Hamlets (40% = 112,000 people @ 240 people/hamlet)
172 Villages (40% = 112,000 people @ 650 people/village)
Urban cities could, in theory, be as large as London. It's more likely the urban population is broken up between the main city and multiple smaller cities. Terrain will ultimately control city size since you can't have a city bigger than the water supply or if there isn't as much farmland. As a general guideline, I'd suggest we follow the population system in the DMG: there are twice as many cities of the next smaller size. So a baseline metropolis would have two large cities, 4 small cities, 8 large towns , and 16 small towns with a population of 99,431.
Take your regional population and divide using the same ratios. For our 102k population we have:
1x Metropolis: 25,647
2x Large City: 12,311 people/city x2=24,622
4x Small City: 5,130 people/city x4 =20,520
8x Large Town: 2,052 people/town x8 = 16,421
16x Small Towns: 924 people/town x16 =14,788
Using the DMG's PC/NPC distribution we know that:
Thorps (containing 14% of the total population) usually have at least one caster, usually a druid, cleric or adept and, with the rare exception of a high level druid or ranger, do not have spell casters above 3rd level. Magic items, even potions and scrolls, are probably unavailable.
Hamlets (28% total population) are a bit better off, likely having both a divine and arcane caster present though neither reaches 5th level (again with the rare druids and rangers). A few common potions or scrolls will likely be available, though they are most likely to be divine healing magics. Expect to wait a day or two for them to be made.
Villages (28% total population) still have arcane casters of 3rd level or below, but divine casters can reach 5th level. Still, about 30% of the villages do not have any 5th level casters. There's a 75% chance you can find the simplest arcane scrolls and the basic healing potions are likely on hand, though not in any bulk.
At this point 70% of the populace is accounted for. Something on the order of 40% of the populace does not have immediate access to 3rd level spells. Less than 5% do *not* have casters in their community.
Small towns (4% of the population) are guaranteed to have more than one arcane and divine caster. Likely you'll have about 3 arcane casters and 10 divine casters. The odds are good that a 5th or 6th level caster lives there. Most low level scrolls and potions can be acquired. There's a decent chance a low-level wand can be commissioned from one of the priests.
Large Towns (4% of the total population) generally have more than a dozen arcane casters, one of which is 5th-7th level. There will be more than 40 divine casters, likely with one 7th-9th level. The majority of potions and scrolls can be had, though it may take a few days. The odds are good you can acquire the simplest magic weapons and armors and the most common wonderous items. Again, expect a wait.
Small Cities (5% of the total population) have 100+ arcane casters and 150+ divine casters with at least one 11th level caster with access to 5th level spells somewhere. Most magic armors can be acquired and a few special types of weapons can be acquired. Virtually all potions and most wands can be acquired in a few days. The vast majority of wonderous items can be had.
Large cities (6% of the total population) will see 600+ arcane casters and 1,000 divine casters. Expect a divine caster of 15th level and an arcane caster of 13th level. A wide variety of magic weapons, virtually all magic armors, potions, wands, wonderous items, and more than a few staves can be found.
The Metropolis (6% of the total populace) has around 2300 arcane casters (~15th level) and over 4,000 divine casters (~17th level). Virtually all but the most legendary magic weapons and armors can be had. All potions and wands can be had and only the most powerful scrolls prove hard to find. Staves and wonderous items of all kinds will be found within the walls.
So what's this mean to the commoner? Most of them know magic armors and weapons are within a singe day's walk. If you have the money, the bishop in one of the Cities can bring a murdered family member back to life. Odds are he sees minor illusions a few times a year at the smaller fairs and if he makes it to the Metropolis for the Grand Fair he will see some spectacle or miracle performed by the archmage or high priest.
On the flip side, the bulk of the populace will never visit someplace bigger than a Large Town more than once or twice since it would take several days away from work.
Everything they need or could want can be had within the Metropolis' domain. Out past the thorpes you reach the wilderness and the dangerous lands filled with monsters. Stories of the horrors out there make you happy to live in such a civilized land. Still, there are stories told by the old folks about the time something burrowed out of the ground and ate the town idiot or a bat-winged terror swooped down and stole an infant from a wagon.
Even if you braved the horrors, the towns are few and far apart because there isn't enough water or decent land, otherwise it would be cultivated. Why bother?