INSTRUCTIONS FOR MAKING FOREST SURVEYS, ETC. 23 



PLANE TABLE. 



For making any map the plane table is the best in- 

 strument in use. Instead of taking notes, as in run- 

 ning compass lines, the surveyor plats his work in the 

 field and can thus always see the progress made. Er- 

 rors and omissions are discovered quickly and rectified. 



The paper upon which the map is to be made is fast- 

 ened to the plane-table board by thumb tacks, and upon 

 it rests the alidade, a straightedge or ruler with fold- 

 ing sights like a compass. From a point on the paper 

 which represents the starting point on the ground over 

 which the table is standing the surveyor draws lines 

 on the paper with the alidade to the various topographic 

 features which are to be mapped. From start to finish 

 of the survey it must at all stations retain the same 

 orientation that is to say, at every station where the 

 table is set up its sides must be exactly parallel to its 

 position at the original station. 



There are several methods, all based upon the same 

 principles. If an isolated block of forest is to be 

 bounded by a survey, the method would be: 



Set up at A with one side of the table bearing ap- 

 proximately north and south. As A is near the south- 

 east corner of the tract, begin to draw at the correspond- 

 ing place on the paper. With the alidade draw a line 

 from A toward B. Measure the distance AB on the 

 ground and scale the proportionate distance on the 

 paper. Set the table at B. With the alidade on the 

 drawn line take a backsight on A. The table will then 

 be oriented or parallel to its position when at A. Draw 

 a line on the paper from B toward C. Measure it and 



