By making the cylinder cut through the Earth at two points, scale errors at extreme latitudes can be avoided. Given a parallel, a cone can touch the Earth at that point. Scale is correct at that standard parallel, but increases progressively on either side of the standard parallel. It is often used for regional mapping. By making the cone cut through the Earth at two points, scale errors at latitudes which are further away from the two standard parallels can be reduced.
Scale is reduced between the two parallels.
A circle plain is made tangent at a given point. This kind of projection is called azimuthal. Meridians radiate as straight lines, and scale increases progressively further away from the azimuthal point. Secant plane To reduce scale errors further away from the azimuthal point, the circle plain can be made secant along a parallel of latitude, or any other small circle. The principle of scale reduction is the same as with the cone.