On the map, the parallels are equidistant arcs of circles. The limiting position for each parallel is the point where the tangent from E touches the parallel. The boundary of the whole projection is therefore a circle, with centre at 45? latitude on the central meridian, and radius length of 45?. To find the limiting longitude for any parallel, since the boundary is at the tangent point (ii) A--sin-1 9o--/9o, where q is in degrees, and from (i) cosec L= cot A cot (.