Nautical charts . o o z P U Q I o cco h z uj O Q. gou o > \-. ;0 Long, $l)y Eaat ° from 190 fcreen.!^, FIG. 25. NORTH POLAR CHART ON ARBITRARY PROJECTION. (77) Arbitrary Projection 79 quality that every straight line on it represents a greatcircle of the earth. To obtain the great circle orshortest course between two points it is therefore onlynecessary to draw a straight line between the pointson a gnomonic chart. Because of the great distortionnear the edges this projection is not otherwise adaptedto navigational use, and it is employed only to markout the general course, and sufficient p
Nautical charts . o o z P U Q I o cco h z uj O Q. gou o > \-. ;0 Long, $l)y Eaat ° from 190 fcreen.!^, FIG. 25. NORTH POLAR CHART ON ARBITRARY PROJECTION. (77) Arbitrary Projection 79 quality that every straight line on it represents a greatcircle of the earth. To obtain the great circle orshortest course between two points it is therefore onlynecessary to draw a straight line between the pointson a gnomonic chart. Because of the great distortionnear the edges this projection is not otherwise adaptedto navigational use, and it is employed only to markout the general course, and sufficient points are thentransferred to a mercator chart. The gnomonic chartis therefore useful in supplementing the mercator chart,supplying its deficiencies as to convenience in markingout great circle courses. The great circle course canbe derived not only more easily and quickly from thegnomonic chart than by computation, but the chart isalso to be preferred because the course marked out onit will show at once if any obstruction, as an island ordanger, is m
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