CS 128/ES 228 - Introduction to Geographic Information Systems

Lab 3: You Are Now Free To Move About The Country (and the Countryside)

Goals:

        By the conclusion of this lab period, you will have:

  1. Learned how to change map projections in ArcMap.
  2. Made qualitative and quantitative observations on three common map projections.
  3. Understood some of the tradeoffs involved in projecting spatial data.
  4. Understood how ArcMap determines the map projection of a Data Frame.
  5. Become familiar with some common coordinate systems used in GIS.
  6. Learned how to add data with different coordinate systems to a GIS.

Course Management Hint

This is a LONG lab.  Some of the write-up can be done without the use of the ArcView system.  It is therefore worth considering whether to take the time to write long answers in your lab or to move on and complete the longer analysis later.  Note that you should obtain all screen snapshots (Steps 6, 7, and 11) and make all ArcView-based measurements (steps 6 and 7) before you leave lab this afternoon.  Note also that this lab makes use of  two data sets.  You may wish to back up the first one to another medium (in case you want to look at it later) before moving on to the second.  You should also begin, starting this week, to make it a habit to back up your lab write-up itself.  While the machines in PL 103 are labeled so you can find the one you used last week (assuming you remember which one it was), they are not ours exclusively and other users may destroy your data.

Let's Take a Trip

  1. Let’s take a trip!   Tired of the campus map?  Open and unzip the data set named Lab 3a and save the resulting files to the GIS folder on the hard drive.  Reset, if necessary, the data sources for the states and cities layers.  Even with both layers present and displaying, you might not be seeing many of the cities – why?  What did you have to do to get all the cities to display?


  2. Why’s Alaska look so weird? The shape of the map may seem odd or distorted to you.  How does the shape of Alaska compare to what you’re used to?  The way ArcMap displays spatial data depends on the coordinate system of the Data Frame.  What coordinate system does the current data frame use?  [Hint]   By the way, what do you suppose “GCS” stands for?  If you’re stumped, try opening the Predefined folder under Select a coordinate system.


  3. Coordinate grids.  It’s easier to visualize the effects of a map’s coordinate system if the coordinate grids are displayed.  This grid is another property of the data frame.  Select the Grids tab and (for now) just accept all the default values.  While you’re messing with the data frame properties, change the name of the data frame to Lab3a.  Close the properties box – did a coordinate grid appear?  No?  The problem is that you’re looking at the map in what ArcMap calls the “data view” and grids are only displayed in “layout view.”  To be fair to ArcMap, it did warn you about this in the Grids box, but who reads these warnings?  How to activate layout view?  We’d recommend asking Help about “Looking at a map in data view and layout view” – you’ll not only get detailed directions but discover a very useful shortcut.  Did you get the grids to display?  It would be a better map if you turned the page setup (under File) from portrait to landscape and then clicked on the map itself and stretched it to fill the page.  Throughout this lab exercise you should zoom and resize at each step to ensure that each map fills the page.  


  4. A map of a different kind.  As you may recall from lecture, there are a bewildering variety of ways of projecting spatial data.  ArcMap lets you use over 60.  There is no such thing as a “best” projection; the best projection to use depends on the location and range of the area to be displayed and the purpose of the map.  Start by changing the Coordinate System to one of the predefined projections, the standard (but much overused) World Mercator projection.  Did the U. S. disappear?  What does the coordinate grid of your map look like in the Mercator projection?  What happens to the size and shape of Alaska?  Since we’re worrying about Alaska, it makes sense to try one of the Polar projections, the North Pole Lambert Azimuthal Equal Area projection.  Again, what happens to the grid?  To Alaska?  Finally, for contrast, switch to the World Robinson, a compromise projection.  Describe the result.


  5. Planning a trip.  Let’s plan two trips, one across Alaska and the other just down from Buffalo to Washington DC and back.  But, while we’re doing the latter, it seems to us that you should visit Milwaukee, given how unaware you seemed to be last week of its charms.  Here is an itinerary for each trip.   Switch back to GCS – North American 1983 HARN datum.  While you’re there, go to the General tab and change the display units to the American favorite for vacation planning, miles. (Warning:  ArcMap tends to revert to meters whenever your back is turned – more precisely, whenever you change the coordinate system.)  Create, a point shapefile called “Cities visited” and a polyline shapefile called “Routes”.  They should both have GCS, N. Am. 1983 coordinates.


  6. Mapping a route.  For each trip, select the cities along the route (including the start/end points) and enter them into the Cities visited shapefile.  You will “find” it easier if you Find and Select each city (once ArcMap has Found an object, it will mark it as selected if you right-click on the object in the Find list and click Select).  Can’t see the city you selected?  Once you’ve saved that file, enter the “legs” of each route into the route file.  At this point, it would help to turn off the cities layer display.  Measure and record the length of each trip (from the starting city around and back to the start again).  You’ll have to zoom in to get good results.  These values will be considered the actual (unprojected) route lengths.  
    7. Capture an image of this map, zoomed appropriately, and include it (in place) in your lab write-up.

  7. Quantifying map distortion.  Change the display to the Mercator, Polar Azimuthal, and Robinson projections.  Repeat the measurements (including capturing an appropriately zoomed image) in each case and compare to the results from the GCS map (previous step).   How did the shape of the route change?  By what percent did the route lengths change (as compared with GCS lengths)?  In general, which projection(s) seem to be preferable for each region of the U.S.?



Fun With Coordinate Systems: Revenge Of The Fire Hydrants

  1. Determining the projection of the Data Frame.  Start ArcMap on one of the lab computers and open, unzip, and save the supplied data set.  Move the cursor around the map and note the coordinates displayed below the map.  Record the coordinates of the center of the intersection of Rt. 417 and Constitution Avenue.  Without peeking at the Data Frame properties, can you guess what coordinate system it is using to display data?  Which of the coordinate systems you learned about in class do they seem to fit?   Okay – having recorded your guess, get ArcMap to tell you the answer.  What did you find out?


  2. Investigating a GIS  data set.  The aerial photographs for the campus map you’ve been using in lab were obtained from a GIS web site maintained by the state of New York.  Go to the site and click on Orthoimagery tab.  We are using the older NAPP (1994-99) aerial photographs, listed below the newer High Resolution images on the navigation sidebar.  Read through the Data Set Description and record the following:  What was the resolution of the photographs?  What type of film was used?  What coordinate system are they projected in?
                For more details, you will have to consult the Metadata file.  Search the Metadata file for the NAPP photographs, using the “Find (on this page)” feature available as an Editing option on most web browsers, and determine the following:  What datum and ellipsoid do they use?  New York State spans 3 UTM zones.  What was done to get photographs from zones 17, 18, and 19 to match?


  3. Adding data with a projection different from that of the Data Frame.  Redo last week’s exercise of adding point locations of some of SBU’s fire hydrants to your map, but stop when the Add XY data query box opens.  What Spatial Reference system has ArcMap discovered?  Change it to geographical coordinates and an up-to-date datum.  Use the cursor to display the coordinates of “Yellow Fellow.”  Compare its map location to the coordinates in its Attribute Data Table and comment.  Discuss what you think ArcMap had to do to make the hydrants appear on the Olean quadrangle.


  4. Adding data from a source with an unknown projection.  Go to the Community GIS web page we viewed in the first class.  [Hint] Open the Town of Allegany GIS and record the locations of the five fire hydrants nearest the intersection of State Highway 417 and Constitution Avenue, including Yellow Fellow.   Create a text file containing the locations, and add to your campus map.  What Spatial Reference system should be used?
                Having trouble finding the new hydrants?  Here’s a hint.  What’s wrong, do you think?  [Hint].  Have the hydrants now shown up on campus?  Good.  Are they where they belong?  If the match is poor, how might you seek to find and remedy the causes?  
                Once you get the new hydrants in the proper locations, change their symbolization so it contrasts clearly with the hydrants added in step 10, change to layout view, zoom and resize the map so as to include all of the fire hydrants, and capture an image of the map display.


  5. What have you learned?  What two errors are commonly made when adding data from a source with an unknown projection?  How are they remedied?

One Last Warning

Ten minute quiz at the start of class tomorrow.  Don't be late!

To Hand In

You are to create a text document including the answers to the questions/discussion requests posed in this lab.  It should include the various screen images at the appropriate place within the text, i.e. adjacent to the answers that pertain to that portion of the lab. Please give it the name GIS Lab 3 – your last names.  Your report should include the two required screen snapshots, zoomed appropriately to show your changes and showing all (and only) the layers you modified in the lab.  The write-up should be turned in, along with a cover page.  Email this document to both instructors (dlevine@cs.sbu.edu and georgian@sbu.edu  ).  We often delete spam with little thought, so give your email a clear and meaningful subject line.

Help Policy

       Help Policy in Effect for This Assignment: Group Project With Limited Collaboration

       In particular, you may discuss the assignment and concepts related to the assignment with the following persons, in addition to an instructor in this course: any GIS instructor and any student enrolled in CS 128/ES 228.

       You may use the following materials produced by other students: materials produced by member of your own group.