Here's a plot of the Pentair Whisperflo pump performance, I have the 1.5 HP pump. Is the Y-axis, Ft. of Water, the vertical distance between the pool and the pump? I'm trying to determine appoximately how many gallons per minute my pump pumps.
No, it is a combination of vertical feet and resistance to flow in the plumbing, measured in vertical feet equivalent. Calculating your dynamic head, the vertical axis on that graph, is something of a black art. This page is a good place to start.
You can also get some information about determining head loss from here. The information on Poolplaza is pretty good but they do make some approximations that are not quite correct. Head loss is not a fixed value but changes with flow rates and pump sizes. The link I gave should help you step through the process. If you have any questions, just let me know.