Certain figures such as arcs and ellipses are centered within a “bounding rectangle,” specified by two points that define the opposite corners of the rectangle. The center of the rectangle becomes the center of the figure, and the rectangle's borders determine the size of the figure. Figure 9.5 shows start and end vectors and a bounding rectangle in which a pie shape has been drawn with the _pie function. The first two sets of coordinates are x1, y1, x2, and y2. They define the boundaries of the rectangle. The pie shape needs two other sets of points, x3, y3, x4, and y4, which indicate the starting and ending lines.