Your projection choice means more than just map display

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How Coordinate System and Projection choice affect ArcGIS Geoprocessing Results. Presentaion by Jesse Wickizer

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Your projection choice means more than just map display

  1. 1. How Coordinate System and Projection choice affect ArcGIS Geoprocessing Results WLIA Conference, 2011 Your projection choice means more than just map display or
  2. 2. 2 Case Studies <ul><li>Large Scale map – parcel selection by buffer </li></ul><ul><li>Small Scale map – Geodesic vs Euclidian buffers </li></ul>
  3. 3. Parcel Selection by Buffer <ul><li>Need list of parcels 1,000 feet from an address </li></ul><ul><li>Using ArcMap for the task </li></ul><ul><li>Using World Street Map ArcGIS Map Service as base map </li></ul><ul><li>Parcel data from Milwaukee County </li></ul>
  4. 4. Add World Street Map ArcGIS Map service
  5. 5. Geocode focus address – 3131 S 29 th St, Milwaukee
  6. 6. Add address point to map
  7. 7. Convert graphic to a shapefile
  8. 8. Create 1,000 ft buffer from address point - default settings
  9. 9. Create 1,000 ft buffer from address point - local coordinate system
  10. 10. Comparison of different buffer outputs
  11. 11. Select parcels that intersect 1 st buffer (Web Mercator) – 126 parcels
  12. 12. Select parcels that intersect 2 nd buffer (SPCS WI South) – 239 parcels
  13. 13. Geodesic vs Euclidian distance <ul><li>Geodesic Distance – distance measured along Earth’s surface </li></ul><ul><ul><li>a.k.a. Great circle distance </li></ul></ul><ul><li>Euclidian Distance – straight line distance between 2 points on a 2D plane </li></ul><ul><ul><li>Measured on the Cartesian coordinate grid of the map projection </li></ul></ul>
  14. 14. Geodesic vs Euclidian distance <ul><li>ArcGIS can create buffers using either distance </li></ul><ul><li>The difference more noticeable at smaller scales and at areas of the map with more distortion </li></ul><ul><li>Example - World map </li></ul><ul><ul><li>Euclidian distance buffers created using Equidistant Cylindrical projection </li></ul></ul>
  15. 19. Questions? Contact: Jesse Wickizer [email_address]

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