Polyconic Projection

In case of a conic projection the picture cone touches or intersects the sphere. That way we get zones of parallels close to the standard parallel(s) with particularly favourable rates of distortions.

Now the sphere can be fractionised for larger regions into several zones of parallels. Each of these zones of parallels will be assigned to a tangent or secant rotation cone. After projecting the zones of parallels onto the particular cone, e.g. according to the equidistant conic projection, the picture cone will be unwinded onto the plane. Thus the parallel circles aren't pictured as concentric circles. We get circular arcs whose centres lie onto the so called »guide line« (cp. figure from [3] under literature). Such projections are called polyconic projections.

           concept of the polyconic projection