The hook
Control networks are the spatial framework for everything else. The full job is designing, observing, adjusting, and publishing control to FGDC and NGS standards. Get this right and every downstream survey is on solid ground.
| FGDC accuracy class | Horizontal at 95% | Typical use |
|---|---|---|
| Class A | < 0.5 cm | Continental geodetic, scientific |
| Class B | < 1 cm | High-order regional control |
| Class C | < 5 cm | Engineering control for large projects |
| 1st-order | ~5 cm | County / city primary control |
| 2nd-order | ~20 cm | Subdivision control |
Memorize these
Concepts that show up on the exam
NGS Bluebooking
Submission process for adding control to the national network. Strict format and metadata requirements; multiple-day occupations typically required.
Network design strength
Number of redundant observations, geometry of baselines. Strong networks tolerate one bad observation; weak networks propagate it.
Constrained vs. minimally constrained
Minimally constrained = hold one station, free up the rest. Tests internal consistency. Constrained = hold all known control. Used to publish final coords.
Error ellipses
Per-station 2D uncertainty from least squares. Direction shows weakest axis; size shows magnitude. Documented for every published station.
Test yourself
How well did it stick?
A quick 5-question check on Control Networks and Geodetic Surveys. See where you stand and what to review.