Geodesy, Coordinate Systems and Projections
Geodetic foundations
Geodesy supplies the reference surfaces and coordinates used by every survey. The geoid is an equipotential surface approximating mean sea level; the ellipsoid is a mathematical surface used for horizontal coordinates. A horizontal datum fixes the ellipsoid, origin and orientation; a vertical datum fixes the reference for orthometric heights. Jamaica has used JAD69 and later JAD2001, while GNSS commonly reports in WGS84/ITRF. The exam tests whether you can keep datum, projection and height systems separate.
Projections and reductions
A map projection transforms latitude and longitude to grid coordinates. It introduces scale factor and grid convergence. Ground distances must be reduced to the ellipsoid and then to grid, or converted using a combined factor. Grid north is not necessarily true north. Heights require h = H + N, where h is ellipsoidal height, H orthometric height and N geoid separation; the sign convention matters.
Worked example
A GNSS receiver reports an ellipsoidal height of 52.30 m. The geoid model gives N = +5.10 m at that point. The orthometric height is H = h - N = 52.30 - 5.10 = 47.20 m. Separately, a ground distance of 1000.000 m with a combined grid factor of 0.9996 becomes 999.600 m on the grid. The reasoning is to apply the height equation and the scale factor explicitly, never silently mixing systems.
Traps
Using JAD69 coordinates as if they were JAD2001; reversing the geoid sign; treating grid distance as ground distance; ignoring convergence when setting out bearings; and applying a 2D transformation to heights.