course mod topic first name date completed
DAT-201 Wk. 2 Classifying data
module learning objectives
  • TR.201.DS.8.A - Maps - Projections
  • TR.201.DS.8.B - Maps - Vector (points, lines, and polys) & raster (bands)
  • TR.201.DS.8.C - Maps - QGIS fundamentals

Map projections

key points

Projection activity sequence

  1. Acquire these materials:
    • A blow-up globe ~6" in diameter
    • 5 sheets of transparency film
    • Clear tape to tape the transparency film together end-to-end
    • Sharpie marker, the finer point the better
    • A 12" ruler
    • A 180-deg Protractor
  2. Create two panels with your transparency film
    • A two-sheet rectangle formed by taping the short ends of two letter-sized sheets of transparency film end-to-end that can be then shaped into a cone hat for the blow-up globe
    • A three-sheet rectangle formed by taping the short ends of THREE letter-sized sheets of transparency film end-to-end that can be shaped into a cylinder whose diameter equals that of the globe
  3. Using strips of clear tape, shape the two-sheet rectangle into a cone whose base is large enough that the blow-up globe's equator fits entirely inside the three dimensional space bounded by the cone. Fix the cone into shape with the clear tape.
  4. Follow the same procedure to create a clear cylinder into which you can slide the blow-up globe. Fix this into shape with clear tape as well
  5. Since CCAC is in the Northern Hemisphere, orient your globe inside each of the projection surfaces such that the continental USA and nearby countries are approximately covered (such that we can project points representing landmarks or borders onto the transparency film. We need to be able to project the same points onto both our cone and our cylinder.
  6. When you have carefully oriented the globe in each projection, transfer major latitude and longitudinal lines from the globe onto each of your projections such that the globe is fixed in orientation inside your projection solid. For example, drawing the 40-degrees north latitude line and the -80 degrees West longitude onto your projections will allow you to position the globe at the northern hemisphere's intersection of these two orienting lines (which is close to Pittsburgh, PA.)

Intro to QGIS & vector mapping

Map projection links:

(Q)GIS help and data sources:

Implications of projections

Question 1: Review the data gathered from the exercise: Which projection system maintains greater angular fidelity? Which maintains greater distance fidelity to the spherical globe? Use data to back your claim.

Question 2: Describe the ideal use cases for each type of projection system given the range of possible uses of a map. (Consider navigation, surveying, representations at various scales, etc.)

Mapping tutorial goal

Count the number of trees points bounded by various geographic polygons in Allegheny County

program requirement 1

Add point and polygon layers to a QGIS map and appropriately symbolize their markers

Use the count points within analysis tool for vector graphics to compare the tree count and density by geographic area

Analysis results

Capture your data in the following table:

Point layer name and description:
Polygon layer name and description:
Polygon 1 ID: Count of points in Polygon 1: Density of points in Polygon 1 (count / area):
Polygon 2 ID: Count of points in Polygon 2: Density of points in Polygon 2(count / area):