26 CHAIN SURVEYING 



CHAIN SURVEYING 



INSTRUMENTS AND METHODS 



Surveying is that branch of civil engineering which treats 4 

 the principles and methods employed for determining the rela 

 tive positions of points on the earth's surface. Surveying i: 

 divided into three general branches, namely, chain surveying, 

 in which no other measuring instrument is employed than a 

 chain or tape for measuring distances; angular surveying, in 

 which angle-measuring instruments are employed in connec- 

 tion with distance-measuring instruments; and leveling, which 

 treats of the determination of elevations, or vertical distances. 



The instruments used most commonly for measuring dis- 

 tances are the engineers' chain, the surveyors' chain, and the 

 steel tape. Marking pins and range poles are used in connec- 

 tion with the chain, especially in measuring long lines. 



The engineers' chain is 100 ft. long and is composed of 100 

 links of steel or iron wire, each two adjacent links being con- 

 nected by small rings. The length of a link, including a ring 

 at each end, is 1 ft. The engineers' chain is used chiefly in 

 railroad surveying, but it is also used to some extent in other 

 kinds of surveying where the foot is the unit of measurement. 



The surveyors' chain, often called Gunter's chain, from the 

 name of its inventor, is the. same as the engineers' chain in 

 every respect, except that its length is 66 ft., or 4 rd., instead 

 of 100 ft. Like the engineers' chain, it is divided into 100 links, 

 and consequently the length of each link is .66 ft., or 7.92 in. 

 This chain is mainly used in land surveying, where the acre is 

 the unit of area. It is very convenient for this purpose, as 

 areas expressed in square chains can be expressed in acres 

 by simply moving the decimal point one place to the left, 

 there being 10 sq. ch. in 1 A. It is also well to remember that 

 there are 80 ch. in 1 stat. mi. 



The surveyors' chain is used in all United States land sur- 

 veys, and whenever the word chain occurs in a legal document, 

 it is understood to mean a surveyors' chain, or 66 ft. 



