1. Understanding Coordinates Ellipsoids, Geoids, Datums and Projections

2. Important concepts for today
What is a Geographic Coordinate System (GCS)?
What is a Datum?
What is a Projected Coordinate System (PCS)?
How do these apply to ArcGIS?

3. A Geographic Coordinate System
Means of measuring spherical coordinates that consists of:
Angular unit of measure
A prime meridian
A Datum

4. Geodetic Datum: Ellipsoid Surface measurements
Reference frame for locations on the surface.
Based on:
Ellipsoid
Surface measurements

5. Shape of the Earth
Sphere
Ellipsoid

6. Axes of the Ellipsoid:
Minor
Major
Axis
Semi - Major
Semi - Minor

7. Earth Geoid:

8. There are different ellipsoids that work best at different areas on earth:

9. Geodetic Datum: Ellipsoid Surface measurements
Reference frame for locations on the surface.
Based on:
Ellipsoid
Surface measurements

10. Local Geodetic Datums

11. Geocentric Geodetic Datums

13. Datum conversions:

14. Importance of Using the Correct Datum
Using coordinates from wrong datum can result in position errors of up to 1 kilometer!

16. What happens when plotted like XY?
Geographic Coordinate System

17. Projected Coordinate Systems:

18. Different surfaces to Project on:

20. Distortion Caused by Map Projections
Shape
Area
Distance
Direction

21. Types of Projections
Classified by the spatial attribute that they maintain
Projection Type
Maintains
Example
Conformal
Shape
Lambert Conformal Conic
Equal Area
Area
Albers Equal Area Conic
Equidistant
Distance
Equidistant Conic
Azimuthal
Direction
Lambert Equal Area Azimuthal

22. Cylindrical projection

23. Conic Projection:

24. Cylindrical Projection

25. Planar Projection:

26. Azimuthal Projections

33. Homolosine – interrupted projection

35. Projections How does ArcGIS handle map projections for data?
Projecting data creates a new data set on the file system
ArcGIS’s projection engine can go in and out of a large number of different projections, coordinate systems, and datums.

37. In ArcGIS: Exercise 5 3 Situations: Data has no projection > Define
Changing the Coordinate System > Project
Do not change the data itself > Change the data frame projection

38. Projecting spatial data sets
ArcToolbox is used for converting data sets from one system to another
Used for going between projections

39. Use these tools today