Lecture 2-Mapping the Earth(1)

# Lecture 2-Mapping the Earth(1) - Latitude longitude UTC...

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Latitude, longitude, UTC

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Unprojected (GCS) Geographic coordinate system Based on spherical coordinates Degrees of latitude and longitude Projected Converts spherical coordinates to planar Set of mathematical equations Projects 3D coordinates to 2D map 2
The geographic coordinate system is the location reference system for spatial features on the Earth’s surface. The geographic coordinate system is defined by longitude and latitude. 3

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11-4 latitude 50° Prime Meridian Longitude = 0° Equator Latitude = 0° -45° 60°longitude longitude Latitude measures the angle from the horizontal. It represents north-south distance from the equator. Earth is divided into 90 degrees of latitude going both northwards and southwards from the equator (0°) to each pole (90° N and 90° S). (Northern positions are considered to be positive (+) and southern positions to be negative (−).) Longitude measures around the circle of the equatorial plane. It represents east-west distance from Prime Meridian. Earth is divided into 180° degrees of longitude going both eastwards and westwards from the prime meridian (0°) until meeting approximately at the international date line (180° E = 180° W). (Eastern positions are considered to be positive (+) and western positions to be negative (−).) + (60°, 50 °) + (-45°, 50 °)
1. not a perfect sphere an oblate (flattened) ellipsoid. 2. experiences bulge at equator due to the speed increase, and oblateness at the poles.

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11-6 50° -45° 60° However, the earth is not a perfect sphere. The actual shape is closer to an ellipsoid. Mapping a point at (-45,60) onto an ellipsoid better represents its position on the earth’s surface than if a sphere were used. Cartography defines the ellipsoid using a major and minor axis representing the longer and shorter radii of the ellipsoid. These values have changed over time as we have developed better measurements of the earth’s shape. True sphere + +
11-7 50° -45° 60° The earth is not a perfect ellipsoid either. It has a topographic surface defined as the change in elevation from…what? From the geoid . The geoid is a theoretical surface defined by gravity measurements. It is described as “the mean ocean surface of the Earth, if the oceans were in equilibrium, at rest, and extended through the continents” (Wikipedia). It is too complex and irregular to use to map points on, so the ellipsoid is used. + + But the discrepancy between the geoid and ellipsoid produces another source of error to locations.

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Matter is not evenly distributed across the planet's surface, and bodies of water are constantly shifting due to winds and currents. Geoid shows the shape that mean sea level would have if it could somehow be extended over the entire surface of the globe
11-9 50° -45° 60° To minimize the discrepancy between the geoid and ellipsoid, a datum is defined.

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