B. Historical Background

Prior to the NAD 83 readjustment C&GS (now NGS) maintained records in written form. Control information was conveyed to users in paper form called datasheets using a simple standardized format.

Figure I-1 is the datasheet for control point Johnson; click here for a pdf version

Figure I-1   Johnson Datasheet

Most control points had a single one-sided datasheet. Because they were not occupied, two third-order intersection stations were commonly included together on a single datasheet sude.

1. Identification

The top of the datasheet identifies the datum, Figure I-2, and point identification, Figure I-3.

Figure I-2 Datum	Figure I-3 Point Identifier

Each point is uniquely is identified by a quadrangle index and number.

QUAD

The quadrangle is 30-minute by 30-minute area identified by its southeastern corner. Digits one and two are the latitude degrees, digits three through five are the longitude degrees. The sixth digit is a quadrant: 1-NE, 2-SE, 3-SW, 4-NW. Figure I-4 is an explanatory note on a Wisconsin State Triangulation Index map.

Figure I-4 Note on State Triangulation Index Map

STATION

The station number is a sequential number, beginning with 1001, within the quad.

Additional information

LATITUDE and LONGITUDE are the extent of the quadrangle.
DIAGRAM is the 2-degree by 1-degree USGS topoquad.

Johnson is point number 1015 in the NW quadrant of the 42°30-43°00' x 89°30'-90°00', Figure I-5.

Figure I-5 Quad 4 of Quadrangle 42089

2. Location and Monument

The left side of the datasheet, Figure I-6, describes the point's general location, monumentation, and accessory information.

Figure I-6 Monument and Location

It may also include observation condition information.

Yup, the targets were set 100 ft above some points and the instrument (and operator) was 25 feet above Johnson.

Historical Note

In order to sight long distances and see above obstructions, instrument and target towers were often used. Various non-standard wooden and metal towers were used until 1926 when Jasper Bibly introduced his namesake steel towers. They were sturdy and designed for transportation, erection, use, and teardown efficiency so were quickly adopted for geodetic surveying. The NGS Historical Photo Archives has some great images of towers and the surveyors brave enough to scale them. If you think centering a total station ~5.5 ft above a ground mark can be a challenge, consider centering a theodolite 100+ ft above a ground mark..

3. Position Information

The right side of the datasheet contains specific position information and connections to other control points.

a. Network information, Figure I-7

Figure I-7 Network Information

Johnson is a first order triangulation station established in 1935.

b. Grid information, Figure I-8

Figure I-8 Grid Information

Multiple coordinates could be shown if the point was near the edge of a zone.
For point Johnson: Wisconsin South SPC zone

Coordinates
Convergence
Grid azimuth to the azimuth mark

c. Geodetic information, Figure I-9

Figure I-9 Geodetic Information

Geodetic coordinates, elevation (if available), and azimuths and directions to other control points observed. Not all control points will have this latter information.
Because Johnson was part of a first order triangulation network, it includes observations to other network points as well as other visible points.