We don't know all the digits of π, but we know it's a little more than 3. Therefore, we draw the point in approximately the right place and then label it:
When the points are not exact and not labeled, we can't do what we did with integer coordinates and go backwards from the graph to the ordered pair. We won't be able to tell the difference between 3, 3.1, 3.14, and π on a number line just by looking, unless you're hanging out with that guy who keeps a ruler on him at all times. It better be an awfully precise ruler.