What is a projection?

# What is a projection?

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## What is a projection?

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1. What is a projection? • A map projection is used to portray all or part of the spherical Earth on a flat surface. This cannot be done without some distortion • Every projection has its own set of advantages and disadvantages. There is no "best" projection • In GIS we must select the one best suited to our needs, reducing distortion of the most important features

2. ChartProjections Three main types LAMBERT (Conic) GNOMONIC (Azimuthal) MERCATOR (Cylindrical)

3. LAMBERT (Conic) projections result from projecting a spherical surface onto a cone.

4. LAMBERT (Conic) Projections • Lambert Conformal Conic projection • Area, and shape are distorted away from standard parallels. Directions are true in limited areas. Used for maps of North America. Lambert Conformal Conic projections are used for rectangular zones with a larger east-west extent. • Ex: North Carolina, Tennessee

5. GNOMONIC (Azimuthal) Azimuthal—Geometrically projected on a plane. Point of projection is the center of a globe.

6. GNOMONIC (Azimuthal)

7. GNOMONIC (Azimuthal) • Used by some navigators to find the shortest path between two points. Used in seismic work because seismic waves tend to travel along great circles. • Any straight line drawn on the map is on a great circle, but directions are true only from center point of projection. Map is perspective (from the center of the Earth onto a tangent plane) but not conformal, equal area, or equidistant. • Considered to be the oldest projection. Ascribed to Thales, the father of abstract geometry, who lived in the 6th century B.C.

8. Mercator • Used for navigation or maps of equatorial regions. • Any straight line on the map is a rhumb line (line of constant direction). • Directions along a rhumb line are true between any two points on map Gerardus Mercator (1512-1594)

9. MERCATOR (Cylindrical) projections result from projecting a spherical surface onto a cylinder.

10. Features of Mercator • Distances are true only along Equator, but are reasonably correct within 15° of Equator. • Areas and shapes of large areas are distorted. • Distortion increases away from Equator and is extreme in polar regions. The map is not perspective, equal area, or equidistant. • Equator and other parallels are straight lines and meet meridians at right angles

11. WHAT IS A NAUTICAL CHART? A Nautical Chart is a graphic portrayal of the marine environment. In addition to its basic elements, a chart is a working document used by the mariner both as a "road map" and worksheet and is essential for safe navigation.

12. Chart Scale The size of the area represented in a chart varies in according to the scale of the chart Charts with a small scale will cover a large area Charts with a large scale will cover a small area 1/1 1/900.000 1/150.000 1/3.000.000 1/100.000 1/40.000

13. TURKISH NAUTICAL CHART GENEL HARİTALAR : 1/600.000 – 1/150.000 PARÇA HARİTALAR : 1/150.000 – 1/50.000 PORTOLONLAR : 1/50.000 den büyük - - two digits - - - three digits - - - - four digits 112 3212 291

14. TURKISH NAUTICAL CHART Turkish Nautical charts are divided 3 region 1 29 2 3

15. 2 1 19 20 3 9 12 16 10 13 11 16 15

16. 14 17 18 9 8 3 19 1 7 6a 6 2 5 4