LAMBERT CONFORMAL CONIC PROJECTION

Figure 9-25.-Lambert conformal conic projection. chart projection. A great circle is any line on the earth’s surface (not necessarily a meridian or the equator) that lies in a plane that passes through the earth’s center. Any meridian lies in such a plane; so does the equator. But any parallel other than the equator lies in a plane that does not pass through the earth’s center; therefore, no parallel other than the equator is a great circle. Now, 1 minute of arc measured along a great circle is equal to 1 nautical mile (6076.115 ft) on the ground. But 1 minute of arc measured along a small circle amounts to less than 1 nautical mile on the ground. Therefore, a minute of latitude always represents a nautical mile on the ground, the reason being that latitude is measured along a meridian and every meridian is a great circle. A minute of longitude at the equator represents a nautical mile on the ground because, in this case, the longitude is measured along the equator, the only parallel that is a great circle. But a minute of longitude in any other latitude represents less than a nautical mile on the ground; and the higher the latitude, the greater the discrepancy. LAMBERT CONFORMAL CONIC PROJECTION The Lambert conformal conic projection attains such a near approach to both directional and distance conformality as to justify its being called a conformal projection. It is conic, rather than polyconic, because only a single cone is used, as shown in figure 9-25. Instead of being considered tangent to the earth’s surface, however, the cone is considered as penetrating the earth along one standard parallel and emerging along another. Direction is the same at any point on the map, and the distance scale at a particular point is the same in all Figure 9-26.-distortion of the Lambert conformal conic projection with the standard parallels at 29 degrees and 45 degrees. 9-22