The US SPCS zones show the decisions made in picking a projection, in this case between the transverse Mercator and the Lambert conformal conic, both conformal projections.

Lambert conformal conic

Transvere Mercator

Other countries have made the same decision about the projection to use for their national maps, based on the shape of the country to choose either the Lambert Conformal Conic or a transverse Mercator.

Last revision 8/29/2018