Reference · 11 pages
Coordinate systems & projections
State Plane, UTM, low-distortion projections, and the grid-versus-ground arithmetic that decides whether a measured distance matches a published one.
- Why projections existYou cannot flatten a curved surface without distorting it. Every projection chooses what to preserve and what to sacrifice — surveyors pay in distance.
- State Plane zonesState Plane exists so surveyors can use plane coordinates over a whole state. Zones exist because a projection can only stay accurate over a limited width.
- Lambert vs TM vs obliqueThree conformal projections cover the United States. A zone's shape decides which it uses, and that decides whether scale varies with latitude or easting.
- Grid scale factorThe ratio between a distance on the grid and the same distance on the ellipsoid. Where it comes from, how it varies across a zone, and how large it actually gets.
- Elevation and combined factorThe elevation factor reduces a measured distance from the terrain to the ellipsoid. Times the grid scale factor it gives the combined factor you actually apply.
- Ground vs gridMultiply to go from ground to grid, divide to go back. The direction of the correction is the most common error in State Plane work, and it is systematic.
- Survey foot vs international footTwo feet differ by exactly 2 parts per million. On a State Plane northing of 2 000 000 ft that is 4 ft of position error, and nothing in the data will look wrong.
- UTMSixty zones, each 6° wide, with a fixed central meridian scale factor of 0.9996. Uniform worldwide, and about ten times more distorted than State Plane.
- Low-distortion projectionsA projection designed so grid distance equals ground distance to a few parts per million over a project area — removing grid-to-ground arithmetic entirely.
- Convergence and the three northsThree different norths, and the angle between the first two is the convergence of meridians. Where it comes from, how large it gets, and the sign people reverse.
- Latitude and longitudeLatitude and longitude, the three notations they are written in, how far a second of arc really is, and the formatting slips that move a point across the planet.
Other sections
All reference- Public Land Survey SystemTownships, ranges, sections and aliquot parts as the BLM Manual of Surveying Instructions describes them — how the rectangular system was laid out, how corners were monumented, and how a retracement follows it.
- Datums & heightsHorizontal and vertical datums, the ellipsoid and the geoid, NAD 83 and NAVD 88, and the modernized reference frames that replace them.
- Survey types & practiceWhat an ALTA/NSPS survey is and is not, boundary versus topographic versus construction work, and the vocabulary a client, an attorney and a field crew each use for the same thing.
- FS exam guideHow the NCEES Fundamentals of Surveying exam is structured, what each subject area covers, and how to build a study plan around it.