[Ed_]

At any point on an ellipse, the sum of the distances to the two foci will always be the same. You can exploit this to draw one pretty neatly--put stakes at the foci, and attach the two ends of a string to the stakes. The string should have just enough slack that, when pulled tight, the point you're pulling reaches the edge. (i.e. longer string = bigger ellipse) Move the foci farther apart to make it longer and skinnier.

Then by pulling the string taut in different directions, you can find your outline. Just be careful not to get it wound around the stakes.

Of course, when the foci move to the same point, the ellipse becomes a circle.