GEO 265 Exercise 3
Exploring Map Projections

using ArcView

Due by start of class 10/17/03

 

Introduction

 

A map projection is a means of transferring information from a 3-D sphere (the globe) to a 2-D plane (a piece of paper or a computer screen). Understanding map projections is important to anyone working with GIS because a three dimensional object cannot be represented perfectly in two dimensions. Some information must be distorted. Map projections allow the mapmaker to select which quality (or qualities) should be preserved in a map. The choice of map projection can affect not only the aesthetics (beauty) of the map but also any analyses performed using that map.

 

This exercise explores several map projections and illustrates how map features are distorted in different ways by different map projections. The exercise focuses on projections designed for world maps but the principles apply to maps of a continent or a single country as well.

 

The ArcView Help system includes a description of all supported map projections as well as help topics on how to set the map projection and other important parameters.  Please read the ArcView Help topics:

In addition, the following help topic is a useful reference: Map scale and accuracy

In this exercise you will:

At the end of the exercise, you are asked to answer questions about the properties of specific projections.

For this lab, please turn in your lab report, including answers to the questions posed in this lab (in bold with a "Q:" for a total of 10 pts).  Also be sure to hand in your lab notebook.  Again, please refer to the course documents for complete guidelines on writing these two documents.

 

 

Getting Started

1.  Start ArcView and create a New Project. 

2.  Set your working directory to your students account and then immediately Save the project to your directory. Call the project ex3_<yourname>.apr

3.  Then add the themes World30.shp, Country.shp and Cities.shp from the directory C:\esri\esridata\World .  Your themes should be ordered Cities.shp, Country.shp and World30.shp in the View Table of Contents from top to bottom so that you can see the features of each theme.  Turn on the themes.  

 

A.  Comparing map projections

1.  Create a world base map including Countries, Major Cities, and Ocean grid

a.  Make the View window active and set the map projection for the view.  Make sure that the Projection Properties Category is Projections of the World and the Type is Geographic. If this is not the case, set these accordingly.

b.   In the View Properties dialog box, check that the Map Units are set to decimal degrees and the Distance Units to miles.  

c.  Set the Theme Properties for the Cities.shp theme to show only a few key cities, such as New York City, Los Angeles, Anchorage, Honolulu, and Sydney.  To do this, select Theme/Properties from the menu.  Click on the Query Builder icon (which is a hammer with a question mark) to open the Query builder dialog box.

d.  In the Field list double click on [Name] to insert it into the text window below.  It will become part of the logical expression that defines your query. Now click once on the equal to operation button. The operator is added to the expression.  In the Values list double click on the name of the city to add it to the query. Continue forming your query by clicking on the OR operator and then reconstructing the next phrase ([NAME]= name of city) for all of the cities that you want displayed.  Pay attention to the syntax.  Click OK to close both dialog boxes.

e.  Notice now that the only cities that are displayed are those you specified in the query above.

 

2.  Create a second base map and set the map projection to Robinson

a. In the project window with the View document type active, click on New.  This will create an empty view (View2) into which you will copy the themes from View1.  To do this make View 1 active and using the shift key make all three themes active.  Then from the Edit menu select Copy Themes.  Now make View2 active and select Edit/Paste. 

b. Set the map projection for the view.  Make sure that the Projection Properties Category is Projections of the World and select the Type to be Robinson. 

c.  Set the Distance Units to miles.

 

3. Create another view and set the map projection to The World from Space

a. Copy and paste themes from View1 to View3 in the same manner outlined above.

b.  Set the map projection properties Type to World from Space and the Distance Units to miles.

 

4. Create another view and set the map projection to Mercator

a.  Repeat step a above copying the themes into View4.

b.  Set the map projection properties Type to Mercator and the Distance Units to miles.

 

5. Compare the maps

Arrange these View windows so you can see all of them and compare the maps:

Q: a. List each projection and describe what appears distorted in each of the Views?

Q: b. Are there obvious limitations to any of the map projections?  What are they?

Hint: Read the ArcView help topics for a description of each projection (Geographic, Robinson, World from Space and Mercator).  

 

B. Customizing a map projection

 

6. Find View3 (The World from Space) and focus the map on Honolulu

a.  Confirm that "The World from Space" is the projection Type. Click the button for "Custom"; enter Honolulu's longitude (-157.8) as the Central Meridian and its latitude (21.3 N) as the Reference Latitude.

 

7. Change the focus of View3 to Sydney, Australia (150.9 E, -33.8 S)

 

8. Change the focus of View3 to Corvallis, OR (-123, 45N). 

 

Q: a. Describe what changes occurred as you changed the Central Meridian and Reference Latitude.

Q: b. Explain why the longitude and latitude values are negative and positive.

Hint:  Again review the information presented as well as references presented in this exercise to help you.

 

C. Map projections and distance

 

9. Measure the distance from New York to Los Angeles in each view and record the distances. 

a.  Use the Zoom In tool on the Tool bar to zoom in closer to the continental US.  Then using the Measure tool, also found on the tool bar, measure the distance between New York and Los Angeles.  With the Measure tool, click on the point location of one city and then double click on the point location of the other city.  In the status bar at the lower left corner of the project window, a Length measurement will appear.

 

Q:  What is your unit of measurement? __________________

Q: View1 _________                    View2_________       

Q: View3_________                     View4_________         

 

10. Create another view (View 5) and select an equidistant map projection, such as Platte Carree, centered on New York City (-74.1 W, 40.7 N)

Q:  a. Measure the distance from New York to Los Angeles and record the value: View5_________

Q:  b. In comparison with View5, which is an equidistant projection ,which of the four Views above gave the "truest" distance? _________

Q: c. When would it be important to use a map projection that preserves distance?

d.  Use the Zoom to Full Extent button tool to return to the full geographic extent of the themes.

 

D. Map projections and shape

 

11. Using the drawing tool, draw several circles on View1

a. With View1 active, use the drawing tool to draw a circle inside one of the 30x30 degree squares of the World30.shp theme.  To do this, select the point drawing tool by clicking on the far right icon in the tool bar (the icon with the dot in it).  This will pull down the drawing tool menu.  Select the icon with the circle.  The mouse will now appear as crosshairs in your view.  Position the crosshairs at the center of one of the 30x30 degree squares.  Click and hold as you move the cursor out towards the edge of the square to create a circle within it.  The circle graphic will be selected after you have created it. 

b. Copy and paste the circle into several more squares by selecting Edit/Copy Graphics and then Edit/Paste.  The graphic will be pasted on top of the original.  You must then select and move the graphic to another location using the Pointer tool.  Position the circles at the equator, mid-latitudes and poles and near the edges of your theme (be sure you are zoomed out to the full extent).  You should have about eight (8) circles positioned throughout the theme.

Q: c. Change the map projection to Mercator. What happens to the circles?________________________

Q: d. Change the map projection to Robinson. What happens to the circles? _______________________

Q: e. Change the projection to another of your choice. List the map projection and describe what happens to the circles? ________________

Q: f. Which of the projections distorted the shape of the circles most severely? ____________________

Q: g. When would it be important to use a map projection that preserves shape/angles? _____________

 

E. Map projections and area

 

12. Change the map projection to Mollweide and record the area of several circles

a. Using the Pointer tool, select one of the circles near the equator and record its area.  You will need to click on the edge of the circle, not inside to select that graphic.  The area reading will appear in the status bar at the lower left corner of the project window. 

Q:      Area of circle near equator______________

Q: b. Select a circle in the mid-latitudes and record its area______________

Q: c. Select a circle near a pole and record its area______________

 

13. Change the map projection to Behrmann; record the area of the same circles

Q: a. Equator ______________ Mid-latitudes ______________ Pole ______________

Q: b. Are the areas of the circles the same as you recorded above? __________ Why?___________

 

14. Change the map projection to Mercator; record the area of the same circles

Q: a. Equator ______________ Mid-latitudes ______________ Pole ______________

Q: b. Are the areas of the circles the same as you recorded above? __________ Why?___________

 

15. Change the map projection to another of your choice; record the area of the same circles.  List the projection:_____________________________________

Q: a. Equator ______________ Mid-latitudes ______________ Pole ______________

Q: b. Are the areas of the circles the same as you recorded above? __________ Why?___________

Q: c. When would it be important to use a map projection that preserves area?

 

F.  Exploring common map projections

 

16.   Using information available to you from the ArcView help topics as well as this

USGS web site (mac.usgs.gov/mac/isb/pubs/MapProjections/projections.html)

answer the following questions in your own words (DO NOT cut and paste!).

Q: a.  Define the following terms:

1.   conformal

2.     equal area

3.     equi-distant

4.     true direction (equi-azimuthal)

 

b.  Some map projections are used more frequently than others are and it is important to know the properties of these different projections. 

 

Q: Using the resources referenced above answer the following questions about the properties of The Globe and these projections: Transverse Mercator, Azimuthal Equidistant (or Equidistant Azimuthal), Lambert Conformal Conic, Albers Equal Area Conic and Stereographic.

1.     Describe their general use and suitability for mapping

2.     Describe the distortions inherent in each projection

3.     List the method of projection for each one (conic, cylindrical, etc.)

 

 

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