Bounding coordinates and polygons for anatomic regions. Distance and position on the rectal wall were entered into the GIS and plotted as points on a two-dimensional plane. The x-axis represents position on the rectal wall, measured in either radial degrees, centimeters, clock-face position, or quadrant. The y-axis represents distance from the dentate line measured in centimeters. Polygons were then created by digitizing from bounding coordinates.