Learning Module: Selecting Spatial References for Spatial Analysis

Purpose

This module exposes you to the various spatial reference systems that are available for performing spatial analysis.

Learning Outcomes

• Define the terms:
  • Projection method
  • PCS
  • GCS
• Select the appropriate projection system based on a region of interest:
  • Geographic
  • Universal Transverse Mercator (UTM)
  • State Plane
  • North American Alber's Equal Area
  • North American Lambert Conformal Conic.
• Demonstrate an understanding that no matter how we project spherical data (3D) onto a plane (2D), there will be distortion.
• List the spatial references that are appropraite, and commonly used, for spatial analysis in Humboldt County.

Reading

• Video: Peter's Projection
• Reading: Chapter 3
  • All except "Datum Transformations", "Vertical Datums", and "Dynamic Heights" only if you really want to!
• Projections of the human head

Presentations/Discussions

• Ellipsoids
  • The Earth is Not a Sphere!
  • Standard Ellipsoids
• Datums
  • Datums Defined
  • Common U.S. Datums
  • Local vs. Earth-Centered Datums
  • Datum Shifts
• Projections
  • Introduction to Coordinate Systems / Spatial Reference Systems
  • Definition of Projecting
  • Projection Families and Methods
  • Projected Coordinate Systems (PCS)
  • Projection Distortion
  • Distortion Exploration Tool
  • Projection Systems:
    • Universal Transverse Mercator
    • State Plane
    • Orthographic
    • Web Mercator
    • Geographic

Activities

Understanding how projections work is a challenge for almost all students. Two methods for getting a better understanding for how we convert spherical data to planar data are:

1. Optional: Find an "American Educational Map Projection Model" and play with the overlays on the globe until you can visualize data on a sphere being "projected" onto the two dimensional overlays.
2. Purchase an inflatable globe and then cut it open along a meridian line (line of longitude). Notice that it will not lay flat. Make additional cuts trying to make the earth lay on a flat surface. This is actually quite difficult even though the globe was created using strips that were originally flat!

Both of these activities help illustrate a key concept that no matter how we "project" data there will always be some distortion.

Additional activities

• Visit the Wikipedia pages for some of the projections described here.

Lab

• "Fun" with Projections