New Topographic Survey Methods 



439 



judgment of the topographer, which may only be attained through 

 considerable experience and some amount of natural talent, often 

 called "topographic sense." 



As the price of stimipage increases, the accuracy and detail de- 

 manded on topographic maps increase. Some of the larger 

 companies now have their strips riui at 2V2-chain intervals, 

 estimating each tree separately and trusting nothing to averages. 



Accuracy of Method — Error of Closure 



The results attained by those who have been working with the 

 Abney method as outlined are truly marvelous. On one project, 

 comprising 54,000 acres in the Coeur d'Alene National Forest in 

 northern Idaho, completed during the 1915 season, 64 miles of 

 control line were run with an average elevation closure of one foot 

 to the mile. 



The area mapped was very rough and mountainous and the 

 timber cover consisted largely of heavy stands of Idaho White 

 pine accompanied by heavy undergrowth and dense brush. The 

 greater part of the area had been previously covered by both the 



