1. Deconstructing Spatial Reference: What Every GIS User Needs to Know Paul Trevillion, Esri

2. You already have a sense of it

3. Spatial Reference = “Spatial Reference System” Coordinate System Projection Datum

4. -117.159271 32.704597 -117.164426 32.708095

8. #1Every spatial data set has a coordinate system File-based data: Shapefiles Raster datasets File geodatabases Personal geodatabases Server hosted data Map services Features services Image layers Web Maps RDBMS-hosted data Enterprise geodatabases Workgroup geodataabases

9. #1Every spatial data set has a coordinate system File-based data: Shapefiles Raster datasets File geodatabases Personal geodatabases Server hosted data Map services Features services Image layers Web Maps RDBMS-hosted data Enterprise geodatabases Workgroup geodataabases

10. #1 Every spatial data set has a coordinate system

11. #2A map has a coordinate system

12. #3Mapping anything on a flat surface is a PROJECTION … -90 +90 +180 -180 0,0 x,y +,+ x,y +,- x,y -,- x,y -,+ Y axis = Prime Meridian X axis = Equator

13. #3Mapping anything on a flat surface is a PROJECTION …

14. #4… even when the coordinates are lat/long degrees (GEOGRAPHIC)

15. #5Every flat map distorts the real world in some way

16. #6For small portions of the earth, we tend to use projections that minimize distance distortion

17. #7These allow us to use linear measures (feet, meters) as coordinate values. These are called PROJECTED COORDINATES

18. #8There are thousands of STANDARD coordinate systems, both GEOGRAPHIC and PROJECTED

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