Lab 3. Measurements in different coordinate spaces


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To start with, we will look at this data layer.  I will release the lab data once I’ve finished talking.

 

I’ve provided a point shapefile called CityPoints_LatLong for you to use in this section. I want you to calculate their X and Y coordinates using UTM17, UTM16, State Plane Georgia East, State Plane Georgia West, and Long/Lat.

You will need to do the following:

  • Add a new field for the UTM17 X coordinate (make it a float type)
  • Add a new field for the UTM17 Y coordinate (make it a float type)
  • Add new fields for UTM16 X, UTM16Y, Ga SP east X, Ga SP east Y, Ga SP west X, Ga SP west Y, Longitude, and Latitude
  • Change the data frame coordinate system to UTM17 – use NAD 1983
    • Use CALCULATE GEOMETRY to calculate the UTM17 X coordinate
      • Use the ‘Coordinate system of the data frame’ in your calculation
      • Make sure you use meters as your unit of measure
    • Repeat for the UTM17 Y coordinate
    • Recall UTM uses meters as its measurement unit
  • Change the data frame coordinate system to UTM16 – use NAD 1983
    • Use CALCULATE GEOMETRY to calculate the UTM16 X coordinate
      • Use the ‘Coordinate system of the data frame’ in your calculation
      • Make sure you use meters as your unit of measure
    • Repeat for the UTM16 Y coordinate
    • Recall UTM uses meters as its measurement units
  • Change the data frame coordinate system to Georgia State Plane east – use NAD 1927 (US FEET)
    • Use CALCULATE GEOMETRY to populate the X and Y coordinates
      • Use the ‘Coordinate system of the data frame’ in your calculation
      • Make sure you use feet as your unit of measure
    • Recall State Plane uses feet as its measurement unit
  • Change the data frame coordinate system to Georgia State Plane west – use NAD 1927 (US FEET)
    • Use CALCULATE GEOMETRY to populate the X and Y coordinates
      • Use the ‘Coordinate system of the data frame’ in your calculation
      • Make sure you use feet as your unit of measure
    • Recall State Plane uses feet as its measurement unit
  • Change the data frame coordinate system to Geographic > World > WGS84
    • Use CALCULATE GEOMETRY to populate the Long/Lat (X and Y) coordinates
      • Use the ‘Coordinate system of the data frame’ in your calculation
      • Make sure you use decimal degrees as the unit of measure
    • Recall Long/Lat uses degrees as its unit of measure

Your next task is to manually calculate the distance from each city to Athens using the UTM17 measurements, UTM16 measurements, SP Ga east measurements, SP Ga west measurements, and Long/Lat measurements – one distance for each coordinate system.

You need to export your attribute table as a text file, load it into Excel and perform your calculations.  This is how…

  • Open your point layer’s attribute table
  • Click on the table options button (in the upper left of the table) > Export…
    • Change the file type to Text File
    • Change your output location
    • Name your output
  • Open your exported text file in Excel and make your calculations
    • Use Pythagorean’s theorem to calculate the distances in UTM17, UTM16, State Plane GA East, State Plane Georgia West, Long/Lat

 

PLEASE UNDERSTAND THAT, IN THIS LAB, THE CONCEPT OF DISTORTION DUE TO YOUR SELECTION OF COORDINATE SYSTEM WAS DEMONSTRATED USING POINTS AND DISTANCE.  YOU WILL EXPERIENCE THE SAME DISTORTION IN AREA MEASUREMENTS AND DIRECTION MEASUREMENTS AND SCALE MEASUREMENTS IF YOUR SELECTION OF COORDINATE SYSTEM IS UNWISE.


 

LAB 3 QUESTIONS (1 – 7, reference lecture materials) (8 – 10, reference your Excel table)

  1. What UTM zone should I use if I am creating GIS data for the state of Alabama?
  2. What UTM zone should I use if I am creating GIS data for a site in western Idaho?
  3. What UTM zone should I use if I am creating GIS data for a site in eastern Idaho?
  4. Assume you are working along the Mississippi/Alabama border.
    1. What UTM zone should you be working in?
    2. At this site, would your easting value (the X coordinate) be larger than 500,000m or smaller than 500,000m?
  5. What does a UTM northing value (the Y coordinate) of 3,000,000m mean?
  6. What State Plane zone should you use if your site is in eastern Georgia?
  7. The State Plane zones for some states are oriented in a north-south direction and others are oriented in an east-west direction. Why are the state plane zones established in this manner?
  8. Consider the four Athens-to-Pittsburgh distances (UTM17, UTM16, SPGaEast, SPGaWest). Which measurement would you present as the most accurate? Please tell me why you made this decision?
  9. Why are the Lat/Long distance measurements nonsense?
  10. Create a table that presents the results from your Athens-to-city distances. The table should contain the to-city, utm17-distance, utm16-distance, SPGaE-distance, SPGaW-distance, and the decimal degree distance.  Round your values to the nearest tenth.  Format your table like this one
    Image result for properly format a table
  11. Flipgrid response (make sure to respond to the ‘Lab 3 Response’ topic):  In today’s lab, you measured the straight-line distance from a handful of cities to Athens, GA. You made these measurements based on XY coordinates measured in the UTM 17 , UTM16, State Plane Georgia East, State Plane Georgia West, and Latitude/Longitude mapping planes. Your distances varied wildly. I would like to know:
    1. Which distance measure do you have most confidence in?
    2. Explain your answer to #1.
    3. What coordinate system would you use if you were tasked with measuring the distance from San Francisco, CA to Portland OR?

UPLOAD YOUR EXCEL file to ELC too.