NJDEP - NJGS - Bulletin 66, Mapping Digest for New Jersey, 1965

HORIZONTAL CONTROL DATUMSThe nationwide net of triangulation arcs was established by the UnitedStates Coast and Geodetic Survey in order to determine precisely thelocations of points on the e_rth's surface by spherical coordinates. Thework was begun in the early part of the nineteenth century, and formany years individual arcs remained unconnected. About 1900, extensionsand connections of the arcs made it possible to compute the entirenet as a single unit. Instead of embarking upon a major adjustmentwhich would have involved recomputing the position of every controlstation, it was decided to adopt the datum which had been used throughoutNew England and along the Atlantic Coast. A considerable amountof recomputatlon was avoided, yet the datum chosen proved nearly idealfor the entire country. Designated the United States Standard Datum,it was based upon Clarke's spheroid of 1866 and originated at stationMeades Ranch in Kansas (Latitude 39° 13' 26".686, Longitude 98 °32" 30".506). Inherent errors in the positions of stations throughoutthe triangulation net balanced out when the latitude and longitude ofMeades Ranch was used as a starting point for computations.In 1913 Canada and Mexico adopted this datum, and in recognitionof the continental significance, the name was changed to North AmericanDatum. By 1927 the national triangulation network was completedto a sufficient degree to allow a major adjustment. Many of the arcsestablished between 1900 and 1927 had been made to fit the existingnetwork, and error distribution was not ideal. In order to correct thissituation the western half of the national net, then the eastern half, werereadjusted. Since station positions were altered up to 1 second in latitudeand 1.4 seconds in longitude, it was necessary to change the name ofthe datum to prevent confusion of new and old positions. The nameNorth American Datum o[ I927 was adopted and represents changes inposition only, since the geographic position of base station Meades Ranchremained unchanged, and Clarke's 1866 spheroid was retained, thusfundamental properties of the net were not altered.Although the positions developed were considered to be final, andthe Atlantic Coast Arc adjustments were completed by 1933, some minorreadjustments have been found to be necessary. During the progress ofthe New Jersey Geodetic Control Survey discrepancies were discoveredbetween two parallel triangulation arcs. In 1937 a first-order baselinefrom Elizabeth to Port Reading was measured, and first-order triangulationchecks were made between Princeton and Netcong by the UnitedStates Coast and Geodetic Survey. The results of this work slightlychanged geographic positions north of a line from Seaside Park to Mt.Holly to Newton to Phillipsburg. Local Control Survey traverses inthe area were then recomputed and in every case closure ratios wereimproved.15NEW JERSEY GEOLOGICAL SURVEY