Page 685 



THE SMOOTH SHEET 



7412 



In plotting by dms. and djjs. do not use the intersections of meridians and parallels 

 to plot from, but use points on the parallels or meridians slightly offset from the inter- 

 sections. A magnifying glass should always be used for setting the dividers on line 

 and for selecting the final position of the station. The beam compass should be used 

 if the distances are too long to plot accurately with dividers. 



06' 



8005' 



■Dp.- 



Back dp. h>J 



16' 



Figure 152 — Control stations plotted by dms. and dps. on a distorted sheet. 



On recently constructed smooth sheets in which there is no distortion, triangulation 

 stations should always be plotted by the dm. and dj). method. The plottings may 

 be checked with the "latitude and longitude scales" (see 7412). 



Other types of control are often plotted by d7ns. and dps., especially when their 

 positions are available only in this form. 



7412. With Latitude and Longitude Scales 



Geographic positions ma}^ also be plotted with latitude and longitude scales 

 (C in fig, 91). These are similar in appearance to a triangular engineer scale, each con- 

 taining one scale for the plotting of latitude and five scales for the plotting of longitude 

 at various latitudes. With these scales a geographic position is plotted by minutes 

 and seconds directly, without recourse to the dms. and dps. 



Each scale covers a distance slightly longer than 1 minute of arc at a scale of 

 1:10,000 and is divided into 60 main divisions, each division being further subdivided 

 into 5 divisions. It is thus possible to plot 0.2 second of arc directly from the divisions 

 and to interpolate to 0.05 second. By placing the scale slightly at an angle to the 

 meridians or parallels, the two ends of the scale may be made to coincide with the two 

 adjacent meridians or parallels, thus dividing the intervening space into 60 equal parts. 

 When a station is to be plotted, the correct latitude should be marked at a slight distance 

 each side of the station, the two points being connected by a fine straight line. The 

 longitude may be similarly plotted, the correct position being at the intersection of the 

 two lines; or the longitude may be plotted directly on the line of correct latitude. 

 (For further description see 4822.) 



