30 



AGRICULTURAL ENGINEERING 



maps are to be prepared, one of the heavy, serviceable papers, 

 like Whatman's hot-pressed paper, is desirable. 



Making the Map. In making a map, the proper scale 

 to use, that is, the ratio between the actual distances in the 

 surveyed tract and corresponding ones for the map, must 

 first be decided upon. In the case of an average-sized farm, 

 100 or 200 feet to the inch is a convenient scale. The larger 

 the area or the smaller the maps the greater will be the dis- 

 tance represented by one inch on the map. If the scale, 

 (meaning the instrument used for measuring) be graduated 

 so as to give 50 divisions to the inch, it will be easy to use 



with any of the ratios proposed. 

 For instance, suppose the ratio of 

 100 feet to the inch be adopted, 

 then one division on the scale will 

 represent 2 feet; and if 200 feet be 

 adopted as a ratio, then one divi- 

 sion will equal 4 feet, etc. 



The handling of the drawing 

 instruments mentioned is simple. 

 The head of the T square, when 

 held by the hand against the 

 straight edge of the drawing board, 

 will permit the drawing of parallel 

 lines. By holding the triangle 

 sides being given. against the blade of the T square, 



all vertical lines may be drawn accurately. The ruling or 

 right-line pen is used in drawing straight lines on the final 

 map with the India ink. 



The first operation to perform in preparing a map is to 

 lay off the boundary of the tract to be mapped. Then the 

 location of other features may be added. Angles may be 

 plotted in by the use of the protractor, if angles have been 



Fig. 12. Laying out a tri- 

 angle, the length of the three 



