BOARD  OF  ESTIMATE AND  APPORTIONMENT

OFFICE   OF  THE   CHIEF  ENGINEER

PRECISE LEVELING IN NEW YORK CITY

By Frederick W. Koop

Assistant Engineer, Board of Estimate and Apportionment.

General Statement.

At a meeting of the Board of Estimate and Apportionment of the City of New
York held on February 19, 1909, a resolution was adopted appropriating the sum
of $10,000 for the running of precise levels and the establishment of bench marks
in connection with the topographical work of all boroughs, and on March 2 this
resolution was approved by the Board of Aldermen. On February 16, 1911, an addi¬
tional $5,000 was voted for the completion of this work, making a total appropriation
of $15,000. From this sum were paid the salaries of the men employed on the work,
office rentals, cost of instruments, railroad fares and incidentals. The salary of the
writer, as Assistant Engineer in charge, was paid by the Board of Estimate and
Apportionment.

When the initial appropriation was secured the writer was directed to carry out
the work and to follow in its execution a plan previously presented by him to the
Chief Engineer of the Board of Estimate and Apportionment. The plan proposed
was as  follows:

(1)     To call on the United States Coast and Geodetic Survey for a list of bench
marks in and around New York City, with their locations and elevations. These
benches had all been adjusted, referred to mean sea level at Sandy Hook and,
though few in number, were to form the basis of future leveling in New York City
and vicinity.

(2)     To make a reconnaissance of each borough, and select the level lines neces¬
sary to give a good level net in each; also to locate suitable points for bench marks
along these lines and to establish others, so that there would be at least one per¬
manent bench mark to each mile of level line.

(3)     To call on the topographical bureaus and other engineering departments of
the city for a list of bench marks along the proposed level lines, with the datum
planes to which they were referred and the history concerning the adoption of such
planes, and to ascertain if possible what other departments or organizations made a
practice of referring their elevations to these datum planes.

(4)     To adopt the methods now in use by the Coast Survey, both in the field
operations and ni the reduction of the notes and office computations, in order to
secure the best results for the city, and to attain a degree of precision in the leveling
at least equal td that attained by the Coast Survey in their precise leveling during
recent years.

(5)     To refer all elevations to mean sea level at Sandy Hook, N. J., which is
the Standard Datum of the United States.