1. Copyright © 2000–2004 ESRI. All rights reserved. Introduction to ArcGIS I Working with georeferenced data

2. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-2 Lesson 8 overview  Georeferencing  Coordinate systems  Datums  Projections and distortion  Projecting your data

3. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-3 What is georeferencing?  Data is referenced to a location on the earth’s surface  Geographic coordinate systems  Projected coordinate systems

4. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-4 Coordinate systems  Geographic coordinate system  Latitude and longitude are not uniform across the earth’s surface  Cartesian coordinate system  Measures of length and angle are uniform - X + Y - X - Y + X - Y X + X + Y Data usually here Y

5. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-5 Datums and datum conversion  A frame of reference for measuring locations on the surface of the earth  Measurements are referenced to a geodetic origin and an ellipsoid model Earth’s surface Local datum NAD27 Ellipsoid CLARKE 1866 Local datum NAD27 Ellipsoid CLARKE 1866 Earth-centered datum NAD83 Ellipsoid GRS80 Earth-centered datum NAD83 Ellipsoid GRS80 Meades Ranch Kansas Earth’s center + +

6. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-6 Referencing locations  Locations on the earth are referenced to the datum  Different datums have different coordinate values for the same location I-10 through Redlands, CA UTM NAD27 UTM NAD83

7. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-7 Map projections  Map projections convert curved surface to flat surface CylinderPlaneCone

8. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-8 Projection distortion  Distortions make geographers SADD Shape Area Distance Direction 3D Earth2D Map

9. Introduction to ArcGIS I Copyright © 2000–2004 ESRI. All rights reserved. 8-9 Types of projections  Generally classified by the spatial attribute they preserve Conformal Equal area Equidistant Azimuthal Shape Area Distance Direction Lambert Conformal Conic Albers Equal Area Conic Equidistant Conic Lambert Equal Area Azimuthal Projection type Maintains Example