Highlight your score and it'll show a tooltip that tells you the breakdown of your score.
Some factors include wonders, population, cities, tech, culture(?)
After all that, your final score is calculated based on how many turns are spent to win, from my observation it is a multiplier that might be an inverse of the amount of turns left in the game.
I don't think difficulty matters that much, nor does the map size (aside from having more room for cities, obviously) have any impact on the final score.
...come to think of it, I've seen differences of my scores between hall of fame (your high scores) and the score of that game (the one that compares you with historical figures), so maybe the HoF score is normalized to prince.
My highest score is 110k from winning a game in 7 turns, needs a bunch of tweaking though, obviously.