Figure 9-25.-Lambert conformal conic projection.chart projection. A great circle is any line on theearth’s surface (not necessarily a meridian or theequator) that lies in a plane that passes through theearth’s center. Any meridian lies in such a plane; sodoes the equator. But any parallel other than theequator lies in a plane that does not pass through theearth’s center; therefore, no parallel other than theequator is a great circle.Now, 1 minute of arc measured along a greatcircle is equal to 1 nautical mile (6076.115 ft) on theground. But 1 minute of arc measured along a smallcircle amounts to less than 1 nautical mile on theground. Therefore, a minute of latitude alwaysrepresents a nautical mile on the ground, the reasonbeing that latitude is measured along a meridian andevery meridian is a great circle. A minute of longitudeat the equator represents a nautical mile on the groundbecause, in this case, the longitude is measured alongthe equator, the only parallel that is a great circle. Buta minute of longitude in any other latitude representsless than a nautical mile on the ground; and the higherthe latitude, the greater the discrepancy.LAMBERT CONFORMAL CONICPROJECTIONThe Lambert conformal conic projectionattains such a near approach to both directional anddistance conformality as to justify its being called aconformal projection. It is conic, rather thanpolyconic, because only a single cone is used, asshown in figure 9-25. Instead of being consideredtangent to the earth’s surface, however, the cone isconsidered as penetrating the earth along onestandard parallel and emerging along another.Direction is the same at any point on the map, and thedistance scale at a particular point is the same in allFigure 9-26.-distortion of the Lambert conformal conic projection with the standard parallels at 29 degrees and 45 degrees.9-22
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