INSTRUCTIONS FOR MAKING FOREST SURVEYS AND MAPS. 



ELEMENTS OF SURVEYING AND MAPPING. 



These simple instructions are issued to members of the 

 Forest Service in order that forest surveys and maps 

 may be as nearly uniform as practicable. They do not 

 include directions for the use of instruments of great 

 precision, and the tables are prepared only to such 

 accuracy as is attained in careful timber cruising or in 

 surveying with the magnetic compass. This is J or 15' 

 of arc. 1 



Forest surveys are made for two purposes to locate 

 and mark lines or boundaries upon the ground, or to 

 furnish data for the preparation of maps. 



The correctness of a survey depends upon the excel- 

 lence of the instruments in use and the skill of the sur- 

 veyor and his party. A skillful surveyor can do better 

 work with poor instruments than an unskilled or care- 

 less one with the best instruments. Small instrumental 



i The "diurnal" or daily change of a magnetic needle, which is one of the variations 

 for which allowance is made in precise surveying, amounts to 10' or 15', and the influ- 

 ence of magnetic storms upon the needle is frequently unsuspected at the time a survey 

 is made. 



Clinometers and clinometer compasses, by which the degree of a slope or a vertical 

 angle may be measured, are generally read only to the nearest \ or \. 



Members of the Forest Service who are using solars, transits, levels, etc., have 

 received training and experience in the care and use of such instruments, and can 

 execute the necessary surveys of precision. They are provided with advanced 

 manuals of surveying and construction, tables, ephemerides, etc. 



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