The external boundaries of a subdivision shall be monumented in the
field by survey markers placed not more than 1,400 feet apart in any
straight line, at all corners, at each end of all curves, at the point
where a curve changes radius, at all angle points along the meander
line, those points to be not less than 20 feet back from the bank
of any river or stream or edge of wetland, except that when such corners
or points fall within an existing street, the survey markers shall
be placed in the side line of the right-of-way.