Surveying, Mapping, and Site Layout
Core concepts
Understand leveling (differential, trigonometric), distance measurement, angle measurement (theodolite/total station), traverse computations (bearings, latitudes and departures, closure), coordinate systems, and setting out (horizontal and vertical control). Know contour maps, slope, and earthwork volume (average end area, prismoidal).
Common traps
- Bearings vs. azimuths: quadrantal bearings require careful conversion; back bearings differ by 180°.
- Traverse closure: a closed traverse should sum to zero in latitudes and departures; misclosure indicates error.
- Leveling: collimation error and curvature/refraction corrections are often ignored in quick problems but matter for precision.
- Earthwork: average end area is an approximation; prismoidal is more accurate for varying sections.
Worked rule of thumb
For a closed traverse, sum of latitudes = 0 and sum of departures = 0. Latitude = distance × cos(bearing angle from north), departure = distance × sin(bearing angle). If the sums are nonzero, apply a compass rule (Bowditch) correction proportional to segment length. For earthwork, volume between two sections = (A1 + A2)/2 × L.
Always check units and sign conventions: north and east are positive; south and west are negative.