# Standard line

From ICA Map Projections

A conformal line of a map projection on which the principal scale is conserved. Along a standard line the Tissot's indicatrix are circles with unit radius. In cylindric and conic projections, and for a spherical model of the Earth, the standard lines are circles. Examples of standard lines: standard parallels in normal cylindric and conic projections; central meridian in transverse cylindric projections.