also: だいけんず
noun
gnomonic chart; great-circle chart; great-circle map
A specialized cartographic term for a chart or map on which great circles appear as straight lines, used in navigation and geodesy.
大圏図は、航空機の最短経路を計画するのに使われる。
Great-circle charts are used to plan the shortest routes for aircraft.
航海士は大圏図を見ながら針路を決めた。
The navigator decided the course while looking at the gnomonic chart.
Mercator projection; unlike a gnomonic chart, rhumb lines (lines of constant bearing) are straight, but great circles are curved.
Compound of 大圏 (great circle) and 図 (chart, map). The term is a direct calque from English 'great-circle chart' or 'gnomonic chart'.