3-10  Lambert Conformal Conic Projection a.  General.  Lambert Conformal Conic Projections are the most widely used projections for civilian mapmakers and surveyors.  Many nations use this projection for civil and military purposes in their country.  The Lambert Conic Conformal Projection can be visualized as the projection of an ellipsoid onto a cone which is either tangent or secant to the ellipsoid.   The apex of the cone is centered in the extension of the polar axis of the ellipsoid.  A cone that is tangent to an ellipsoid is one which touches the ellipsoid at one parallel of latitude ; a secant cone will intersect the ellipsoid at two parallels, called Standard Parallels. This text will discuss the secant condition.  See Figure 3-14.        STANDARD PARALLELS (SECANT LINES) POLAR AXIS Figure 3-14  Secant Condition of Lambert         Conformal Conic Projection b.  Plane of Projection.  When the cone of projection is flattened into a plane, meridians appear as straight lines radiating from a point beyond the mapped areas; parallels appear as arcs of concentric circles which are centered at the point from which the meridians radiate. See Figure 3-15.  None of the parallels appear in exactly the projected positions; they are mathematically adjusted to produce the property of conformality.  This projection can also be called the Lambert Conformal Orthomorphic Projection. Figure 3-15  Cone Flattened onto a Plane c.  Secancy of the Ellipsoid.  The parallels of latitude on the ellipsoid which are to be secant to the cone are chosen by the mapmaker.  The distance between the secant lines is based on the purpose and scale of the map.  For example, a US Geological Survey (USGS) map depicting the 48 contiguous states will use standard parallels located at 33° N and 45° N latitudes (12° between secant lines); aeronautic charts of Alaska use 55° N and 65° N (10° between secant lines); and for the National Atlas of Canada the secant lines are 49° N and 77° N (28° between secants).  The standard parallels for USGS maps in the 7.5 and 15 minute series will vary from state to state, several states are separated into two or more zones with two or more sets of standard parallels.  See Figure 3-16. d.  Distortion.  Since this is a conformal projection, distortion is comparable to that of the Transverse Mercator and Polar Stereographic Projections. Distances are true along the standard parallels and reasonably accurate elsewhere in limited regions. Directions are fairly accurate over the entire projection. Shapes usually remain relative to scale but the distortion increases away from the standard parallels. Shapes on large scale maps of small areas are essentially true. e.  Scale Factor.  Scale factor is exact (unity or 1.000) at the standard parallels.  It decreases between and increases away from the standard parallels; the exact number is dependent upon the distance between the standard parallels. 3-11  Oblique Mercator Projection a.  General.  The Oblique Mercator Projection is actually many different projections using variations of the Transverse Mercator.  All are cylindrical and conformal; however, instead of the cylinder being transversed 90° from the Mercator Projection, it is transversed at an angle which places the long axis of the cylinder 90° from the long axis of the area being mapped.  In other words, if the general direction of an area that is to be mapped lies in a northeast/southwest attitude, the cylinder of projection would be transversed 45° west of north.  The cylinder is usually DRAFT 3-10