The best known transverse cylindrical projection is the Transverse Mercator. Figures 1 and 2 illustrate that the Mercator and Transverse Mercator projections are dissimilar. The UTM projection and grid were adopted by the U.S. Army in 1947 for designating rectangular coordinates on large-scale maps for the entire world. The Earth, between latitudes 84 N. and 80 S., is divided into 60 zones, each 6 wide in longitude. Rectangular grids have therefore been developed for the use of surveyors.
Grids are appropriate even when powerful digital computers are available.
In large raster images, it is convenient to arrange the rows and columns of image pixels in alignment with an accepted surveying grid. Most image display software depends on a simple relationship between image coordinates and screen coordinates. Grid systems are normally divided into zones so that distortion and variation of scale within any one zone are kept small. Zones of the UTM are bounded by meridians of longitude, but for the SPCS, State and county boundaries are used. This is true of both printed paper maps and digital cartographic products.