The Circle tool lets you construct a circle in three different ways.

  • You can define the center first and then a circumference point
  • You can define a circumference point first and then the center
  • or you can define the circle with two opposite circumference points.
You use the second Option Button to control this construction method. The third option button allows you to constrain the second point so that it’s perfectly horizontally aligned or vertically aligned with the first or so that it positioned along a vector you define using the Mark Button. There is one more construction option that will be invisible to you at the time of construction but is still very useful: the number of Snapping Points on the circumference of the circle. This is controlled by the first option button. These are invisible points evenly spaced along the circle that allow you to snap other paths directly to them. See Snapping for more information. Here’s an example of circle construction: