Without having any more info about the points and their interaction, scientifically speaking, you have to connect the points using straight lines, which, by definition, produces a graph with its maximum on one of such a graph.

With this in mind, you can use the following method to find the maximum point:

• Pick two points, and find the slope of the connecting line.
• Compare this slope to the slope of the line connecting point 2 with point 3.
• Continue until the slope turns negative.
• The last point still giving you a positive slope is the maximum of your data set

This, of course, is an algorithm approximating a derivative, which is what you would want to do to find a maximum of a graph in the first place. However, since, as I've explained, the maximum will have to be on a data point, you should simply be able to sort the data points and get the maximum that way. I hope this helps at least somewhat.