Exploring Error and Uncertainty Related to Datums and Projections Using ArcGIS

Skill Drill: Evaluate and Measure Distortion

Table of Contents

  1. Exploring Error and Uncertainty Related to Datums and Projections Using ArcGIS
  2. Skill Drill: Setting Up Your Workspace
  3. Skill Drill: Downloading Data from Natural Earth
  4. Skill Drill: Connect to Your Workspace Folder in ArcMap
  5. Creating a File Geodatabase
  6. Creating Feature Classes from Shapefiles
  7. Adding XY Data using the ArcCatalog Window
  8. Skill Drill: Creating Indicatrices Using the Buffer Tool
  9. Evaluate Distortion Patterns in Map Projections
  10. Measuring Scale Distortion
  11. Skill Drill: Evaluate and Measure Distortion
  12. Troubleshooting Datum Shift
  13. Repairing Corrupted Data Using the Define Projection Tool
  14. Skill Drill: Repairing Incorrect Coordinate System Definitions

Repeat the steps for changing the projection of the data frame and evaluating distortion patterns for the following map projections:

  • Cylindrical Equal Area (world)
  • Goode Homolosine (Ocean)
  • Mercator (world)
  • North America Lambert Conformal Conic
  • North Pole Azimuthal Equidistant

Note: The last two map projections are not in the World folder. Instead, you should look in the Continental folder and the Polar folder respectively.

For consistency, change the central meridian or longitude of center to 180 for each map projections (Figure 2.45). You should measure the distance from Tokyo and Vancouver across the Pacific Ocean.

Figure 2.45: One some map projections, this setting is called the Longitude of Center, while in others, it is called the Central Meridian. The effect is the same. Double-click or tap twice to view the image in a larger size.

Be sure to take screenshots of each map projection. You may place them all into the same Microsoft Word document. Also, you should write down the answers to the same questions for each as well.

With Tissot’s indicatrices, you may only be able to determine distortion patterns in area and shape. Do not worry about distance, direction, or continuity.

  1. Which of the five properties appear to be preserved based on the size and shape of the indicatrices?
  2. Which of the five properties appear to be distorted based on the size and shape of the indicatrices?
  3. Where on the map does there appear to be minimal distortion?
  4. Where on the map does there appear to be the most distortion?
  5. What does the scale factor indicate in terms of distortion for this map projection in the region between Tokyo and Vancouver?

Additionally, you should record each distance measurement from Tokyo and Vancouver on your Excel table (Figure 2.46).

Figure 2.46: This table records the differences in Kilometers between the three-dimensional geodesic measurement and the two-dimensional planar measurements of map projections. Double-click or tap twice to view the image in a larger size.

Be sure to save both your Microsoft Word document and your Excel workbook when done. Be prepared to discuss your answers to the questions and your measurements at a later time.