Type of Pictures of the Main Circles and the Horizontal Circles

According to the type of pictures of the main circles and the horizontal circles we distinguish between two general kinds of projection:

True Projection  (conical projection)

Assuming normal position of the projection axis we have:

  1. The pictures of the main circles (e.g. meridians) are straight lines.
  2. The pictures of the horizontal circles (e.g. parallel rings) are either straight lines or (concentric) circles.
  3. All lines intersect each other rectangularly.

Untrue Projection  (non-conical projection)

Projection for which at least one of the rules above is not true.