The most simple Conic projection is tangent to the globe along a line of latitude. This line is called the standard parallel. The meridians are projected onto the conical surface, meeting at the apex, or point, of the cone. Parallel lines of latitude are projected onto the cone as rings. The cone is then "cut" along any meridian to produce the final conic projection, which has straight converging lines for meridians and concentric circular arcs for parallels. The meridian opposite the cut line becomes the central meridian.
In general, the further you get from the standard parallel, the more distortion increases. Thus, cutting off the top of the cone produces a more accurate projection. You can accomplish this by not using the polar region of the projected data. Conic projections are used for midlatitude zones that have an east–west orientation.
Somewhat more complex Conic projections contact the global surface at two locations. These projections are called Secant projections and are defined by two standard parallels. It is also possible to define a Secant projection by one standard parallel and a scale factor. The distortion pattern for Secant projections is different between the standard parallels than beyond them. Generally, a Secant projection has less overall distortion than a Tangent projection. On still more complex Conic projections, the axis of the cone does not line up with the polar axis of the globe. These types of projections are called oblique.
The representation of geographic features depends on the spacing of the parallels. When equally spaced, the projection is equidistant north–south but neither conformal nor equal area. An example of this type of projection is the Equidistant Conic projection. For small areas, the overall distortion is minimal. On the Lambert Conic Conformal projection, the central parallels are spaced more closely than the parallels near the border, and small geographic shapes are maintained for both small-scale and large-scale maps. On the Albers Equal Area Conic projection, the parallels near the northern and southern edges are closer together than the central parallels, and the projection displays equivalent areas.
- Learn more about the Equidistant Conic projection
- Learn more about the Lambert Conic Conformal projection
- Learn more about the Albers Equal Area Conic projection