I had the same article Jake posted book marked to explain crosspoints.
But to answer @06Honda 's question... Menu A7 on the d7200 only selects how many points you see in the viewfinder for the purpose of jogging around the the initial focus point.
"Choose the number of manual focus points available for manual focus-point selection in the viewfinder."
In other words, it cuts down the viewfinder clutter and lets you more quickly get the initial focus point to the top, bottom or sides of the viewfinder.
This will limit you if you are using single point focus- what you see is what you get. But for the other focus modes, it just gives you a lower selection of starting points to more quickly jump around. The camera should still be able to use the number of points as determined by your focus mode setting. So if you have d51 selected with the focus mode button but your a7 is set to 11, you still have 51 points available but only 11 choices to choose from as a starting point in the viewfinder. The d500 has similar under a6. The choices are 55 or 15 points.