LEARNING ABOUT MAP PROJECTIONS

OVERVIEW

Students will learn how different map projections are used to view Earth. They use an "on-line" map generation tool to discover how well the commonly used Mercator Projection represents high and low-latitude areas. They will also see a map projection used by many scientists: the Mollweide Projection.
 

CONCEPTS

  • Mercator projection maps are commonly used to represent our three-dimensional, globe-shaped Earth on flat, two-dimensional map.
  • Mercator Projection maps are not well-suited for maps whose area covers many degrees of latitude.
  • Other map projections are used by scientists who look at the "whole earth" simulataneously
 
 

MATERIALS

  
     
 

PROCEDURE

 

Preparation

  • Briefly discuss how Earth's geography is given in a coordinate system made up of latitude and longitude.
  • Compare a world map and an Earth globe. Note the differences in how lines of latitude and longitude are represented.
 
 

Activity - Step 1 "About Mercator Projection"

1. On a "Mercator projection," lines of latitude are parallel to each other and lines of longitude are also parallel to each other. So latitude and longitude are perpendicular.

  

Questions - Step 1

  1. Look at an Earth globe. Are lines of latitude parallel to each other? Are lines of longitude parallel to each other? [HINT: At Earth's poles, which lines intesect... latitude or longitude? Do parallel lines ever intersect?]
 
 

Activity - Step 2 "The 'Greenland Problem'"

  1. Most people are accustomed to using Mercator projection maps. Although this projection is fine for many purposes, it's not the best way to represent an area that covers many degrees of latitude. For example, southern Greenland (near the north pole) is actually smaller than the Arabian peninsula (near the equator).
 
 

Questions - Step 2

  1. Why does southern Greenland (red box, above) look bigger than the Arabian peninsula (middle of green box, above) in Mercator projection maps?
 
 

Activity - Step 3 "True View of Earth"

1.At right (>>>), the earth is viewed as a hemisphere ("hemi" is "half" in Latin and Greek). Because our spherical planet has not been "flattened" onto a map, the relative sizes of landmasses is not distorted.

2. Yellow boxes outline the two areas we are going to compare in this Mercator Projection:

  • southeastern U.S.
  • Antarctic peninsula.

3. Click here to learn more about this image.
 
 

Activity - Step 4 "Create a 20° by 20° Map of the Southeastern U.S."

At the "Coastline Extactor" website, you will choose a 20 degree latitude by 20 degree longitude area as follows:

1. Under the "Geographic Range of Extracted Coastline," type in the northermost latitude as "40".

2. Type in the westernmost longitude as "-95" (NOTE: For this map-making tool, negative longitude is west of Greenwich).

3. Type in the easternmost longitude as "-75".

4. Type in the southernmost latitude as "20".

5. Using the "pull down menu" under "Coastline data base," choose the option: "WCL (World Coast Line) (designed for 1:5,000,000)". Or you can choose another data base if you want a more detailed map.

6. Leave the rest of the "clickable" buttons alone.

 

Coastline Extractor

Geographic Range of Extracted Coastline (decimal degrees, west negative) :

 
 
Northernmost latitude
40
 

 
Westernmost longitude:
-95
-75
Easternmost longitude
 
Southernmost latitude
20
 

Coastline data base :
WCL (World Coast Line) (designed for 1:5,000,000) V

Compression method for extracted ASCII data:
None GNU GZIP UNIX Compressed ZIP

Coast Format options:
Mapgen Arc/Info Ungenerate Matlab Splus


Coast Preview options:
No preview Quick Plot GMT Plot

 

Extract the Coast:

SUBMIT
 

7. Hit "SUBMIT" to "extract the coast." (After you've hit "SUBMIT," you may get a "warning message" that says "Any information that you submit is insecure..." Hit "OK" to continue.)

8. Your map will appear as an image on top. Latitude and longitude data, formatted as two columns, are called "XXXX.dat." ( XXXX is a number generated by the program itself.)

9. Print the map.
 
 

Activity - Step 5"Create a 20° by 20° Map of the Anarctic Peninsula"

At the "Coastline Extactor" website, you will choose another 20 degree latitude by 20 degree longitude area as follows:

1. Your two latitudes of interest are "-55" and "-75".

2. Your two longitudes of interest are also "-55" and "-75" (REMEMBER: For this map-making tool, negative longitude is west of Greenwich).

3. Think carefully and then fill your data on the website (shown as "???" at right >>>).

4. You'll get an "error message" if you've entered data incorrectly.

5. Using the "pull down menu" under "Coastline data base," choose the option: "WCL (World Coast Line) (designed for 1:5,000,000)". Or you can choose another data base if you want a more detailed map.

6. Leave the rest of the "clickable" buttons alone.

Coastline Extractor

Geographic Range of Extracted Coastline (decimal degrees, west negative) :

 
 
Northernmost latitude
???
 

 
Westernmost longitude:
???
???
Easternmost longitude
 
Southernmost latitude
???
 

Coastline data base :
WCL (World Coast Line) (designed for 1:5,000,000) V

Compression method for extracted ASCII data:
None GNU GZIP UNIX Compressed ZIP

Coast Format options:
Mapgen Arc/Info Ungenerate Matlab Splus


Coast Preview options:
No preview Quick Plot GMT Plot

 

Extract the Coast:

SUBMIT
 

7. Hit "SUBMIT" to "extract the coast." (After you've hit "SUBMIT," you may get a "warning message" that says "Any information that you submit is insecure..." Hit "OK" to continue.)

8. Your map will appear as an image on top. Latitude and longitude data, formatted as two columns, are called "XXXX.dat." ( XXXX is a number generated by the program itself.)

9. Print the map.

Questions - Step 5

  1. Compare the two maps you've generated.
    • Which is longer? Why?
    • Which is wider? Why?
  2. Think about the range of longitude each map covers.
    • How would the two maps "line up"? (In other words, do these areas lie directly above / below one another, left / right of one another, or both?)
    • Given that the Antarctic Peninsula lies just south of South America, does the result surprise you?
  
 

Activity - Step 6

  1. This activity has shown that Meractor Projection maps are not well-suited for maps whose area covers many degrees of latitude. For this reason, scientists who study the global earth prefer to use map projections such as the "Mollweide projection" (shown below, VVV). [Map is from University of Wisconsin-Madison's Space Science & Engineering Center .]

Questions - Step 6

  1. How does a "Mollweide Projection" differ from a Mercator Projection?
  2. How does a "Mollweide Projection" differ from a hemispheric projection?
    • Click here to see an example of a hemispheric projection.
    • Why is a hemispheric projection not suitable for scientists who study the "whole earth" simultaneously?
  3. Are lines of latitude parallel on a Mollweide Projection? What about longitude lines?
  4. How does the Mollweide Projection "handle" the relative sizes of southern Greenland (red "square") and the Arabian peninsula (green square)?
 

EXTENSION

  • Use a world map to locate another coastline area to "extract" using the "Coastline Extractor" website. They may wish to choose an area that is west of the International Date Line.
  • Complete the "Extracting A Coastline" activity.
  • Research some other types of map projections. For each type discovered, determine the following:
    • What makes that map projection unique?
    • Who uses that type of map projection?
  • Complete the "Map Projections" activity (hosted at the Gulf of Maine Aquarium website).
  
 

VOCABULARY

  • latitude: location on Earth's surface based on angular distance north or south of the equator. Equator, 0°; North Pole, 90°N; South Pole, 90°S.
  • longitude: distance (expressed in degrees) east or west of the prime meridian, along which Greenwich, England is located. The International Date Line is 180° away from the prime meridian.
  • perpendicular: a line or plane at right angles to another line or plane.
  

Atmospheric water vapor is an important factor in determining local weather and global climate. This 1995 image of atmospheric water vapor captures hurricanes which are forming off of Africa's west coast and others moving across the Atlantic toward the east coast of the U.S. The white and light blue areas contain the most water vapor, while the dark areas are the driest. The small bright areas are storms and hurricanes. The big spirals show large-scale circulation patterns in Earth's atmosphere.

[Image available from NASA Goddard Space Flight Center's Scientific Visualization Studio website at http://svs.gsfc.nasa.gov/]: