Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . i3S> 20 30 10 50 60 70 80 90 Fig. 131.—Mercators ConicalProjection. 60 70 80 C 50 ^^^ i40 SO 20 w>. 10 ~-x\\^ 0 ~ZS\\^\^ ii J\-^^ \ 60 70 80 90 100 110 12^ Fig. 132.—Equivalent ConicalProjection. from the apex of the cone at equal angles, while the parallelcircles are equal-spaced circular arcs with the same apex ascenter. (Fig. 130.) In Mercators conical projection the dis-tortion is diminished by making the cone pass through two par-allels of the a
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . i3S> 20 30 10 50 60 70 80 90 Fig. 131.—Mercators ConicalProjection. 60 70 80 C 50 ^^^ i40 SO 20 w>. 10 ~-x\\^ 0 ~ZS\\^\^ ii J\-^^ \ 60 70 80 90 100 110 12^ Fig. 132.—Equivalent ConicalProjection. from the apex of the cone at equal angles, while the parallelcircles are equal-spaced circular arcs with the same apex ascenter. (Fig. 130.) In Mercators conical projection the dis-tortion is diminished by making the cone pass through two par-allels of the area to be represented, so that two parallels of thesphere, instead of one, coincide with their pictures. (Fig. 131.)This is the projection on which the maps of our common atlases 4i6 MAP 120° 115° 110° 105° 100° 96° 90° 86° 80° IS 70° Fig. 133.—Bonnes Projection. and geographies are drawn. Lamberts equivalent conical pro-jection is based on an intersectingcone, and the distances of theparallels increase with increaseof latitude at such rate that themeshes included by them and themeridians show the same areasas on the sphere. (Fig. 132.) Bonnes projection is a pro-jection on the tangent cone inthe center of the map, the parallel curves being drawn in thesame way as in the ordinary conical projection. On these par-allel curves, on both sides of the meridian, the parallel degreesare marked in their true size, and the points of intersection arejoined by steady curves which give the meridians. (Fig. 133.) 184. Constructing a Polyconic Projection.—The polyconicprojections is that best suited to accurate topographic or geo-graphic mapping as it corresponds most nearly to the spheroidalshape of the earth. It is the projection of a series of cones parallelto each
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