formula to factor interior sq. ft. from a length of perimeter ft. with no lenth & width measurements

formula to factor interior sq. ft. from a length of perimeter ft. with no lenth & width measurements   (11/29/2012, 12:51 PM)

I need to determine square ft. and acreage from a survey map with scaled line drawings of forested areas. The areas are in various shapes and sizes.I am unable to make accurate width and length measurements because of odd shapes. Is there a formula for using the known distance in ft. around the area and determining the sq. ft. within that area?