How to drop points from a data series for presentation?
Indeed this problem isn't a very simple one to deal with, despite looking very easy to conceptualise. There exist a certain number of techniques for "reducing" the number of points of timeseries, one being called "downsampling".

A little litterature : https://skemman.is/bitstream/1946/15343/3/SS_MSthesis.pdf

hope this helps,

Cheers