•ArcGIS terminology•Define projection.Specify the projection for some data without changing the data.•Project.Change the data from one projection to another. dr gemson, IIAEM, JU, Bangalore49* ArcGISis a geographic information system (GIS) for working with maps and geographicinformation. It is used for creating and using maps, compiling geographic data, analyzing mappedinformation,sharinganddiscoveringgeographicinformation,usingmapsandgeographicinformation in a range of applications, and managing geographic information in a database.

Types of Coordinate Systems•(1) Global Cartesian coordinates (x, y, z) for the whole earth•(2) Geographic coordinates (, , z) •(3) Projected coordinates (x, y, z) on a local area of the earth’s surface•The z-coordinate in (1) and (3) are defined geometrically; in (2) the z-coordinate is defined gravitationallydr gemson, IIAEM, JU, Bangalore50

Global Cartesian Coordinates (x,y,z)OXZYGreenwichMeridianEquator•dr gemson, IIAEM, JU, Bangalore51

Geographic Coordinates (, , z)•Latitude () and Longitude () defined using an ellipsoid, an ellipse rotated about an axis•Elevation (z) defined using geoid, a surface of constant gravitational potential•Earth datums define standard values of the ellipsoid and geoiddr gemson, IIAEM, JU, Bangalore52

Shape of the EarthWe think of the earth as a sphereIt is actually a spheroid, slightly larger in radius at the equator than at the polesdr gemson, IIAEM, JU, Bangalore53

EllipsePF2OF1abXZAn ellipse is defined by:Focal length = Distance (F1, P, F2) isconstant for all pointson ellipseWhen = 0, ellipse = circleFor the earth:Major axis, a = 6378 kmMinor axis, b = 6357 kmFlattening ratio, f = (a-b)/a ~ 1/300dr gemson, IIAEM, JU, Bangalore54

Ellipsoid or SpheroidRotate an ellipse around an axisOXZYaabRotational axisdr gemson, IIAEM, JU, Bangalore55

Standard Ellipsoids of EarthEllipsoidMajoraxis, a (m)Minoraxis, b (m)Flatteningratio, fClarke(1866)6,378,2066,356,5841/294.98GRS806,378,1376,356,7521/298.57Ref: Snyder, Map Projections, A working manual, USGSProfessional Paper 1395, p.12dr gemson, IIAEM, JU, Bangalore56

Horizontal Earth Datums•An earth datum is defined by an ellipse and an axis of rotation•NAD27 (North American Datum of 1927) uses the Clarke (1866) ellipsoid on a non geocentric axis of rotation•NAD83 (NAD,1983) uses the GRS80 ellipsoid on a geocentric axis of rotation•WGS84 (World Geodetic System of 1984) uses GRS80, almost the same as NAD83dr gemson, IIAEM, JU, Bangalore57

Definition of Latitude, (1) Take a point S on the surface of the ellipsoid and define there the tangent plane, mn(2) Define the line pq through S and normal to the tangent plane(3) Angle pqr which this line makes with the equatorial plane is the latitude , of point SOSmnqprdr gemson, IIAEM, JU, Bangalore58

Cutting Plane of a MeridianPMeridianEquatorplanePrime Meridiandr gemson, IIAEM, JU, Bangalore59

Definition of Longitude, 0°E, W90°W(-90 °)180°E, W90°E(+90 °)-120°-30°-60°-150°30°-60°120°150°= the angle between a cutting plane on the prime meridianand the cutting plane on the meridian through the point, PPdr gemson, IIAEM, JU, Bangalore60

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