Modified Polyconic projection was devised by Lallemand of France, and in 1909 it was adopted by International Map Committee (IMC) in London as the basis for 1:1,000,000-scale International Map of the World (IMW) series.
All meridians are straight.
Parallels are circular arcs. The top and bottom parallels of each sheet are nonconcentric circular arcs.
The top and bottom parallels of each sheet are nonconcentric circular arcs. The two parallels are spaced from each other according to the true scale along the central meridian, which is slightly reduced.
Scale is true along each parallel and along two meridians, but no parallel is standard.
International Map of the World (IMW) series until 1962.
The projection differs from ordinary Polyconic in two principal features: all meridians are straight, and there are two meridians that are made true to scale. Adjacent sheets fit together exactly not only north to south, but east to west. There is still a gap when mosaicking in all directions, in that there is a gap between each diagonal sheet, and either one or other adjacent sheet.
In 1962, a U.N. conference on IMW adopted Lambert Conformal Conic and Polar Stereographic projections to replace Modified Polyconic.
See Polyconic for more information.