Population is vital for a high base score. Check out the difference it makes:
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In 1955, I'd just conquered Saladin, but most of England and Arabia were still in revolt. So I had a fair amount of land to gain. I also had a few techs left to go plus future techs and a couple of wonders left to build. Despite that, the majority of the score increase (2200 out of 3200) between 1955 and 2050 was due to my population growth.
It's entirely possible that someone else will have got an even higher score by founding "junk" cities in every possible location within their empire to get more population points. I think I founded 3 extra cities in the early 80s, but left it at that. I was short of time... in the end, I probably should have invaded Shaka with a turn or two to go. He had some nice, large cities! But by that time it was very late and I just wanted to get it over with.
For reference, my cities in 2050:
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