# MODERN NAVIGATION

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## MODERN NAVIGATION

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Lecture Notes

- Pages:
- 11
- School:
- Massachusetts Institute of Technology
- Course:
- 12 215 - Modern Navigation

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12 215 Modern Navigation Thomas Herring tah mit edu http geoweb mit edu tah 12 215 Today s class Map Projections Why projections are needed Types of map projections Classification by type of projection Classification by characteristics of projection Mathematics of map projections 10 19 2009 12 215 Lec 11 2 1 Need for Map Projections Basic need is because the Earth s surface is curved and so it is not possible to represent on a flat surface with out some distortions Flat surfaces were needed so that people could carry maps with them still a major use With GPS maps are now often represented in a computer in 3 D form or as ellipsoidal coordinates thus minimizing the distortion The amount of distortion depends on the area to be represented over small areas the Earth is nearly flat 10 19 2009 12 215 Lec 11 3 Types of map projections Map projections are classified either by way the projection is made and the surface onto which it is projected or by the characteristics of the resultant projected maps Some projection surfaces are planes cones and cylinders each of these surfaces can be un wrapped into a flat surface Some map projections are purely mathematical so that they can minimize distortions We will deal mathematically with only projection from a spherical body Most accurate map projections are projections from an ellipsoidal body 10 19 2009 12 215 Lec 11 4 2 Projection by characteristics The general characteristics of map projections are given by Conformality When the scale of a map at any point on the map is the same in any direction the projection is conformal Meridians lines of longitude and parallels lines of latitude intersect at right angles Shape is preserved locally on conformal maps Distance A map is equidistant when it portrays distances from the center of the projection to any other place on the map Direction A map preserves direction when azimuths angles from a point on a line to another point are portrayed correctly in all directions Area When a map

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