Arcs

Arcs are a little more interesting than straight lines. You identify the end
point of the line using the ArcSegment.Point property, just as you would
with a LineSegment. However, the PathFigure draws a curved line from the
starting point (or the end point of the previous segment) to the end point of
your arc. This curved connecting line is actually a portion of the edge of an
ellipse.

Obviously, the end point isn’t enough information to draw the arc because
there are many curves (some gentle, some more extreme) that could
connect two points. You also need to indicate the size of the imaginary
ellipse that’s being used to draw the arc. You do this using the
ArcSegment.Size property, which supplies the x radius and the y radius of
the ellipse. The larger the ellipse size of the imaginary ellipse, the more
gradually its edge curves.