in both. (North American Datum of 1983 [NAD 83] and WGS 84 are the same). Mean Sea Level of
1929 (MSL 29) is used for vertical control points. The continental United States (CONUS) uses the
Basic horizontal-control networks are usually established by first-order geodetic
triangulation, precise traverse, or GPS. The lines of the basic network are spaced throughout
a country at intervals of about 96 kilometers.
Basic vertical-control networks are established throughout the country by first-order
differential leveling in areas spaced from 90 to 160 kilometers apart. Permanent benchmarks
(PBMs) are spaced at intervals of about 3 kilometers on these lines.
Supplementary horizontal-control networks are usually established by second-order survey
techniques. These supplementary networks are used to fill in the areas between the basic
control lines. Ultimately, either a basic or a supplementary network station will be spaced at
intervals of about 6 to 16 kilometers.
Supplementary vertical-control networks are established by second-order differential
leveling. These lines are run within the basic control arcs to provide planned control-line
spacing at intervals of about 10 kilometers. PBMs are emplaced on these lines at intervals of
about 2 kilometers.
Horizontal auxiliary-control networks are usually established by second- or third-order
survey techniques. They provide localized control to be used by surveyors for artillery
control, construction engineering surveys, mapping projects, or other positioning
requirements. As more states and other agencies require geodetic accuracy for boundary and
property surveys, they will use these networks.
Auxiliary vertical-control networks are established by third-order differential leveling and are
used to provide localized vertical control. They are also used to support artillery,
construction, and engineering projects.
PART G - SURVEY EQUIPMENT
2-10. Conventional Survey Equipment. Topographic surveyors have theodolites, levels, and
electronic distance-measuring equipment (EDME) in their equipment inventory. The AISI provides
topographic surveyors with the capability to extend control in a timelier and more efficient manner. The
AISI is a total station that combines angular, distance, and vertical measurements into a single electronic
instrument that is designed to digitally record and transfer data into a computer.