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## What is a projection?

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**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**ChartProjections**Three main types LAMBERT (Conic) GNOMONIC (Azimuthal) MERCATOR (Cylindrical)**LAMBERT (Conic) projections**result from projecting a spherical surface onto a cone.**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**GNOMONIC (Azimuthal)**Azimuthal—Geometrically projected on a plane. Point of projection is the center of a globe.**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.**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)**MERCATOR (Cylindrical) projections**result from projecting a spherical surface onto a cylinder.**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**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.**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**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**TURKISH NAUTICAL CHART**Turkish Nautical charts are divided 3 region 1 29 2 3**2**1 19 20 3 9 12 16 10 13 11 16 15**14**17 18 9 8 3 19 1 7 6a 6 2 5 4