Topographic Maps General - 6 of 7
Topographic Maps General FAQs - 7 Found
At the bottom of every USGS topographic map is a diagram that displays the difference and direction between True North (represented as a "star" symbol) and Grid North (abbreviated as "GN").
True North refers to geodetic or geographic north pole, and the lines of longitude converge in the Lambert Conformal Conic projection used on USGS 7.5-minute maps. The star symbol indicates true or geographic north and the star and line in the map diagram point to the north geographic pole.
Grid north is a navigational term referring to the direction northwards along the grid lines of a map projection. In the UTM projections, all north-south lines run parallel to one another.
Because USGS topographic maps mix the UTM and conic projections, occasionally the UTM grid will appear at a small angle to the neat lines of the map.
Military people, who work with UTM grids all the time, tend to rely on grid north. Scientists in the field, who are more likely to use the UTM grid only for recording locations, might opt to use whatever is most convenient.