1. Representing Geography

2. Datum Defines the size, shape, and orientation of Earth Provides.. – Origin: starting place that allows coordinates to be meaningful – Clearly defined surface that the coordinate system is applied to. – No datum = playing checkers without a checkerboard – Defined by an ellipsoid model

3. Ellipsoid Models Provide a reference for the datum and contribute to the datum’s definition Requires survey measurements to define the shape of the earth Clarke 1866 Ellipsoid became the standard reference model for NAD27 Geodetic Reference System of 1980 is the figure for NAD83 X

4. Datum Realization Creation of the physical network of reference points on Earth NGS established network of bronze disks

5. Datum Error Errorless in abstract (when not connected to reality) – no distortion – every point has a unique and accurate coordinate Error introduced when applied to reality – cannot measure perfectly from origin – ambiguity of finding center of objects

6. NAD83 Improved based on survey accuracy advances – GPS – Remote Sensing

8. Coordinate Systems Where are we? – 8800 Grossmont College Drive, El Cajon, CA 92020 – Building 30, Room 252 – 32 ° 49’ 00.7”N Latitude 117 ° 00’ 27”W Longitude – UTM, Zone 11, 0499297 Easting 3630983 Northing

9. Coordinate Systems Cartesian Coordinates – Rene Descartes (latin: Renatus Cartesius) first used graphs to plot/analyze math functions setup rules for 2-D coordinate system – Basis for UTM system, State Plane Geographic Grid – Spherical Grid System (illustrations)illustrations

10. Data Representation All spatial data converted to digital form is represented as… – Points – Lines – Areas (polygons) Discrete Objects vs Continuous Fields

13. Classification of Data