# t7 - Geography 231 Introduction to Geospatial Methods Topic...

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1 Geography 231 Introduction to Geospatial Methods Topic 7: Georeferencing I: Projections and Coordinate Systems Goals Review of geographic coordinates Review of geographic coordinates Introduction to the types of projections Gain a basic understanding of the distortions inherent in projections Expand understanding of UTM

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2 Earth Coordinate Geometry Angular measures, similar to cartesian geometry Sexagesmal scale Circle divided into 360 degrees Degree divided into 60 minutes Minute divided into 60 seconds 55°44’05”N lat; 110°15’32” W long Parallels of Latitude Reference is the Equator Ranges from 0-90 degrees N and S The equator is a great circle; other parallels are small circles
3 Meridians of Longitude Unlike latitude, there is no natural fixed reference point Reference (prime meridian) is the British Royal Observatory in Greenwich, England Ranges from 0-180 degrees E and W All meridians are great circles Great Circles and Loxodromes Plane forming a great circle always bisects the spherical surface Great circles always bisect other great circles Arc segments on great circles form the shortest distance between two points on a sphere Lines on the globe that follow a constant compass bearing are called loxodromes

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4 Graticule The lines latitude and longitude grid drawn on a map or globe Map Projections: Why We Care Orderly system of parallels and meridians used to draw a map on a flat surface Distortion must occur when transforming when transforming information to a flat surface
5 The Projection Process The Geometry of the Earth The earth is an oblate spheroid Oblateness is caused by centrifugal force due to rotation

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6 Geodesy Earth contains areas of bulges and depressions caused by irregular distribution of crustal rock For the purposes of cartography, earth’s shape is described by a reference ellipsoid Ellipsoid A geometric shape (ellipse) described by the shape of its major and minor axes Ellipticity (flattening) given by: f = 1-(b/a) Where: a = semi major axis b = semi minor axis Typical reference ellipsoids have f values between 1/297 and 1/298
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t7 - Geography 231 Introduction to Geospatial Methods Topic...

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