APPENDIX B 



The guide is prepared by drafting concentric circles to represent areas of 1, 5, 10, and 

 20 acres at the average scale of the photos being used. Radii for the circles are easily calcu- 

 lated from (1) the formula for the area of a circle (A - Jtr^), and (2) the average photo scale. 

 For example, the radius of a 1-acre circle is calculated thus: 



A = Ttr^ = 43,560 square feet 



r^ = 43,560 ~ 3.1416 = 13,866 square feet 



r =118 feet 



This can be converted to distance on the photo itself by the relationship: 



Radius on photo „ 



— ; r- = Photo scale 



Radius on ground 



For a 1-acre circle at a photo scale of 1:20,000 this becomes 



Radius on photo _ 1 



118 feet 20,000 

 -: Radius on photo = 118 feet ~ 20,000 = .0059 foot 



Radii for a lake size guide applicable to 1:20, 000-scale photos are as follows: 



Area Radius on photo 



1 acre 0.0059 foot 



5 acres .0132 foot 



10 acres .0186 foot 



20 acres .0264 foot 



A simple method of putting the circles on transparent material is to photograph them and pre- 

 pare a positive transparency. 



20 



