Snap Angle

As you drag the cursor away from the center point, the rotation of the polygon will "snap" into a series of fixed angles. This makes it possible to create a series of shapes with the exact same orientation on the map (eg, a series of rectangles with sides that are all perfectly aligned with the cardinal directions). This field controls the size of the angle between each of the consecutive rotations.

For example, if you set a snap angle of 30 degrees, it will only be possible to orient the shape in a couple of different ways; as you decrease the angle, the rotation becomes and more granular, and at 0 the snapping is completely disabled.