64 ENGINEERING FOR LAND DRAINAGE. 



topography of the ground or to locate needed drains. 

 It is better to keep this work platted up every day, for 

 while the notes are fresh in the mind, quicker and bet- 

 ter work can be done in mapping than if the notes 

 alone must be relied upon. While the notes may and 

 ought to be quite full, the memory enlivens the view 

 and enables one to add that to the descriptive map 

 which will be of value. If there should be no plat of 

 the tract, the boundary should be run in with the com- 

 pass if it is desired to have a complete map in every 

 detail. All maps should be made carefully to a scale, 

 the practical value of which will appear when it is de- 

 sired to make estimates from them for further work. 



Record of the Work, 



The engineer now wishes to put his work on record 

 so that he can plan future location surveys intelligently 

 or represent the capabilities of the tract plainly to 

 others, which latter consideration is very important. 

 For this purpose the plat should be transferred from 

 the field-book and drawn to a convenient scale upon a 

 sheet of paper and the necessary items entered. Re- 

 cord the elevations directly upon the map at the loca- 

 tion where the levels were taken. Indicate water- 

 courses, ponds, trees, etc., by conventional signs. 

 (Fig. 23.) Sketch in dividing lines on water-sheds and 

 indicate surface slopes by arrows. Designate each 

 drainage-basin which has a distinctive outlet as a drain- 

 age section by the letters A^ B, C, etc. 



The work thus far done forms a geography of the 

 tract which shows its natural drainage slopes. The 



