Size could determine proficiency bonus.
Village +2
Town +3
Small city +4
Large city +5
Megalopolis +6
(I'm mentioning cities but you could do this for kingdoms too.)
It would only be added for things where size matters. E.g.:
Str/Might: a bigger city can afford more trained soldiers.
Dex/Subterfuge: a bigger city might have a larger spy network or cooperative thieves guild.
Con/Welfare: a bigger city has more people and is better able to absorb losses and may have bigger food stores.
Int/Knowledge: a bigger city is more likely to have the sages and experts needed, and has bigger libraries.
Wis/Economy: a bigger city has deeper pockets.
Cha/Influence: a bigger city has more people to spread its ideas and new ideas may penotrate more slowly.
Furthermore you could apply it only when the city is "proficient" in the check. Like a city not known for magic might not get the bonus on Int checks for magical lore. Conversely you might give cities Expertise (double proficiency bonus) for areas where they excel.
Maybe for every non-proficient area the city gets to pick an expert area. This would be an easy way to distinguish cities qualitatively. E.g., Strengths: navy, trade, religion; Weaknesses: arcane magic, farming, social mobility.
Including the proficiency bonus lets you use the regular DCs of 10/15/20.
Village +2
Town +3
Small city +4
Large city +5
Megalopolis +6
(I'm mentioning cities but you could do this for kingdoms too.)
It would only be added for things where size matters. E.g.:
Str/Might: a bigger city can afford more trained soldiers.
Dex/Subterfuge: a bigger city might have a larger spy network or cooperative thieves guild.
Con/Welfare: a bigger city has more people and is better able to absorb losses and may have bigger food stores.
Int/Knowledge: a bigger city is more likely to have the sages and experts needed, and has bigger libraries.
Wis/Economy: a bigger city has deeper pockets.
Cha/Influence: a bigger city has more people to spread its ideas and new ideas may penotrate more slowly.
Furthermore you could apply it only when the city is "proficient" in the check. Like a city not known for magic might not get the bonus on Int checks for magical lore. Conversely you might give cities Expertise (double proficiency bonus) for areas where they excel.
Maybe for every non-proficient area the city gets to pick an expert area. This would be an easy way to distinguish cities qualitatively. E.g., Strengths: navy, trade, religion; Weaknesses: arcane magic, farming, social mobility.
Including the proficiency bonus lets you use the regular DCs of 10/15/20.