- international modified polyconic projection
- A modified polyconic map projection chosen by an international committee in 1909 for construction of maps of the whole world, except polar caps, on one projection and on a scale of 1:1,000,000. The size of the sheet is 4° change of latitude by 6° change of longitude from 60°N to 60°S, and 4° change of latitude by 12° change of longitude from 60°N/S to 88°N/S. In this projection, every parallel is a standard parallel. Hence, adjacent sheets fit north to south, and meridians are straight lines converging to the pole of the hemisphere. Each sheet has two meridians correct to the scale, resulting in reduced scale errors. The scale is correct along the bounding parallel and the two standard meridians—it contracts between these meridians and expands outside them. The angles and the bearings are nearly correct and so are the shapes. A great circle is a curve convex to the nearest pole, but it can be treated as a straight line since the maximum distance of the great circle between two points from a straight line joining them is 1 NM on a single map sheet. A rhumb line is a curve concave to the pole of the hemisphere. It is nearly a straight line; the maximum distance from a straight line is 4 NM.International modified polyconic projection.
Aviation dictionary. 2014.