Why is correlation proportionate to the area of the intersection of the areas under the curves of the series?

by Toph   Last Updated August 26, 2018 01:19 AM

I've been staring at this diagram from Wikipedia, trying to understand (particularly autocorrelation):

visualization of autocorrelation

I see that the autocorrelation seems to be proportionate to the overlap between the graphs of the two series. But it's not clear to me why that is. And I don't know how well it generalizes, or what the diagram is assuming.

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