Original: The Poincaré disc model , also known as the conformal disc model , also employs the interior of a circle , but lines are represented by arcs of circles that are orthogonal to the boundary circle , plus diameters of the boundary circle .
Simplified: The Klein model , also known as the projective disc model and Beltrami-Klein model , uses the interior of a circle for the hyperbolic plane , and chords of the circle as lines .