[dlcarrier]

By playing with model inputs, to find a set of input conditions which will create outputs which that historic records.

It's one of those things that is much more precise than accurate, which means that the data on the 1877 map is all plus or minus a range that most of the data falls into. It's like election polls that show candidates a percent or two ahead or behind, but the data is all plus or minus a larger percentage. It gives a general idea of the state of things, but isn't useful for specifics, so it could tell which types of candidates are winning, but is useless at guessing whether any individual candidate will win or lose.