I do think about local populations.
1 million inhabitants is equivalent to about one nation, or one vast city.
The amount influence (fame, recognizability) that a player character has depends on level. I tweaked an earlier formula.
Fame = 10^([L+2]/2)
At level 0 (background), the character will be well recognized by about 10 people. Whether they will be popular or not depends on Charisma and behavior.
At level 1: fame is about 30 noters
At level 2: fame is about 100 noters
At level 3: fame is about 300 noters
At level 4: fame is about 1000 noters
Levels 1 thru 4, start about 20, and correspond roughly to college students, the Student tier.
Professional tier: Level 6, 10,000 (a town), Level 8, 100,000 (a city)
Master tier: Level 10, 1 million (a nation), Level 12, 10 million (an empire)
Grandmaster tier: Level 14, 100, million (larger than the Roman Empire), Level 16, 1 billion (a species)
Legend tier: Level 18, 10 billion (a planet), Level 20 (unavoidably famous across the multiverse)
The corollary is also true.
A town of about 10,000 citizens can be expected to have a few citizens reach up to around level 6 (and its CR equivalent).
A nation of about of about a million has a few members of about level 10 (compare Beowulf). These can show up randomly from any town or village within the nation.
And so on.
The world setting is generally low-levelish. Player characters gain higher levels at a freakish pace. Other high tier NPCs also exist, but are rare, and make some sense their populations.