3-1 General a.    In general, a map projection is a method of repre- senting a portion of the earth's surface on a flat surface. This procedure causes distortions of different types; therefore, many different projections have been developed for use dependent on the size of the area being mapped, the map scale, and the intended use of the maps.  See Tables 3-1, 2, and 3 at the end of this section. b.  A map is a graphic representation of a portion of the earth projected onto a plane surface.  An ellipsoidal surface; however, cannot be flattened onto a plane without distortions of such properties as distance, angle, direction, shape, and size.  For example, an orange peel cannot be flattened onto a table without tearing; if the skin could be flattened and not tear, the areas farthest away from the center would stretch causing distortion.  The same is true with a map projection. c.  Many types of map projections exist, each preserving certain properties and distorting others. Most projections are either cylindrical, conical, or azimuthal; projecting an ellipsoid onto either cylinders, cones, or plane surfaces.  These surfaces may be tangent to the ellipsoid, or they may be secant.  A projection is tangent to the ellipsoid when only one point or line of the projection surface touches the ellipsoid.  It is secant when two points or lines touch the ellipsoid.  See Figure 3-1. d.  One common characteristic applies to all US military maps; they are all based on a conformal projection.  This means that the shape of any small area of the surface mapped is preserved unchanged.  A more stringent definition is that a conformal map projection is one that at any point, the scale is the same in any direction.  Also, the angle between any two lines DRAFT 3-1 Figure 3-1  Projection Types; tangent and secant CHAPTER 3 PROJECTIONS AND GRIDS     Portions of the world have been mapped by different nations since the earliest times of man's exploration of the earth.  These early maps were crude and inaccurate by our standards but sufficed for their intended purpose.  As mans world grew and the need arose for maps covering extensive areas or with better accuracies, cartographers devised methods of projecting the earth onto a surface which could be flattened with little distortion in angles, distances, shapes, and sizes depending on the intended use of the map.      Section I MAP PROJECTIONS CYLINDRICAL; TANGENT CYLINDRICAL; SECANT CONICAL; TANGENT CONICAL; SECANT AZIMUTHAL; TANGENT AZIMUTHAL; SECANT