CHAPTER VI. 



OFFICE WORK. 



The office work of the topographers consists in the reduction and trans- 

 fer of the work from field sheets to the original maps. The reduction is 

 universally effected by photography, this method having been found the 

 most accurate and economical way of effecting it. 



The original sheets are to serve as the original record of work and as 

 manuscript for the engraver. To answer these purposes, they are made 

 complete in all respects as to hydrography, hypsography, and public cul- 

 ture. Every original sheet contains within itself all matter which is to be 

 engraved or placed on record, except as hereafter noted. 



While it is entirely unnecessary that these sheets be fine specimens of 

 the draftman's skill, they are workmanlike in appearance, clear, and legible. 



The original sheets are commonly drawn upon the scale upon which 

 they are to lie published, in order that the engraving may be done directly 

 from the original maps rather than from photographs of them. Frequent 

 departures are, however, made from this rule, to meet other requirements. 



The contour intervals differ widely in different parts of the country, 

 ranging from 5 feet up to 100 feet. Where the scale is 1 : 62500 the com- 

 monest contour interval is 20 feet. In Florida and Illinois the contour 

 interval is reduced to 10 feet, while in the low alluvial regions of southern 

 Louisiana it is only 5 feet. 



With a scale of 1:125000 the contour interval in the Appalachian 

 mountain region is 100 feet, in the Piedmont region it is 50 feet, and upon 

 the Atlantic plain 20 feet, while in the Dismal swamp of Virginia and North 

 Carolina it has been set at 5 feet. With the same scale in Missouri, Arkan- 

 sas, and eastern Kansas the contour interval is 50 feet, while in western 

 Kansas in more recent work it is 20 feet. In Texas the contour interval 

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