Location of existing rock outcrops, high points, watercourses,
depressions, ponds, marshes, wooded areas, single trees not in wooded
areas with a diameter of six inches or more as measured three feet
above the base of the trunk, and other significant existing features,
including previous flood elevations or watercourses, ponds and marsh
areas, if such information is available, or can possibly be determined
by survey.