CS 128/ES 228 - Introduction to Geographic Information Systems

Lab 8: Beginning Spatial Analysis

Goals:

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

  1. Confronted the limitations of ArcMap as we have used it thus farm.
  2. Learned how to use Personal Geodatabases to overcome some of these limitations.
  3. Solved a miniature version of your semester project.

A Disclaimer 

Reviewing what we can (and cannot) do

  1. Buildings revisited.  Open "the usual data frame" and focus upon the Buildings layer.  (Note: it does not matter whether you have the "old" buildings layer from Lab 6 (and earlier) or the "new" one from Lab 7.  If you have both, the "old" one is slightly preferable here.)  Our goal is to compute the areas of two buildings, Murphy and Doyle, as best we can.  First, do so by using measurement tools in ArcMap.  Describe carefully how you are doing this and come up with your best estimate for the area of the footprint of the building.  This estimate may not be very accurate, but that's part of the point.  Be sure to include both the estimate and the method you used to obtain it in your lab write-up.  Having done this, now look at the attribute data.  Record its "estimate".
    2.  

Getting ArcMap to do (some of) the work for you

  1. Personal Geodatabases - or "More than just a pretty face".  If the GIS is to be more than just a display technology, then it must help you compute various quantities.  Two obvious quantities that it can help you compute are lengths and areas.  And, yet, as Step 1 showed, this is not easily done.  To perform calculations of this sort, the data must be properly stored within the computer.  One way to achieve this is to store the information in a Personal Geodatabase, i.e. a database of geographic information that you create.  [There are also multi-user geodatabases, but they appear later in the process - and probably not at all in this course.]  Our goal is now to create a personal geodatabase for the buildings layer.
    1. Start ArcCatalog. Select the folder in which you wish the geodatabase to reside; right click and choose New:Personal Geodatabase. Name it appropriately. (The icon is a gray cylinder.) Right-click on this and choose to make a New:Feature DataSet. Name it appropriately. (The icon is three overlapping gray rectangles.)
    2. Start ArcToolbox. Start the (Conversion Tools:Import to Geodatabase:) Shapefile to Geodatabase Wizard. Use the browser to select the shapefile you desire to convert, (Buildings). Click Next. For the output, choose the dataset you made in Step 1. Then choose the defaults.
    3. Return to ArcMap. Add your new dataset to the map.

    Using your new layer, determine the areas of our two favorite buildings?  How did you do this?  How accurate were the previous estimates?  Can you explain any discrepancies?  Don't you wish you knew about this in Week 1?
    2.  
  2. Creating Geodatabases 'from scratch'. It is possible to create a Personal Geodatabase without having an existing layer.  We will now do this to create one that stores lines rather than polygons.
    1. Using ArcCatalog, make a New:Feature Class. Name it, and go to the next screen. Click Next to get to the third screen. Click on the word “Geometry” (next to Shape in the second row). A new table should open up at the bottom. The third property is “Geometry Type”. Click on Polygon and a drop-down menu appears. Choose Line. Now set the coordinates. WARNING: THIS IS YOUR LAST CHANCE TO DO THIS; OTHERWISE YOU MUST START OVER. To do so, click the gray button labeled “…” on the last line of the field properties (labeled Spatial Reference). Then choose the X/Y domain tab and put in the correct coordinate values. (Don’t know them? Look them up on a layer in your map.)  This is also a good time to set your projection, although that setting can be modified later.  
    2. Add your new dataset to the map.

    Using the editor, add a few lines corresponding to steam pipes.  In particular, add a line from the power plant towards Francis Hall.  This line should cross Rob-Fal, and make a significant crossing of Doyle.  Do not, of course, let this line cross the wetlands!  (For now, you may accomplish this by terminating the line shortly after it leaves Doyle.)  Also add lines to Shay and to Plassmann.  Let these lines cross whatever buildings makes it easy.

  3. Computing more complicated quantities with geodatabases.  Alas, just as you finished drawing in these lines, Congress passed a law which will require that all lines be covered with duct tape.  As a first approximation, Bonaventure will assume that the cost is directly proportional to the length of these lines.  What is the total length of these lines?  Find a way to compute this that would work just as well for one hundred lines as for three.  [In other words, don't do any computations yourself.]  A hint is available. 

    After further thought, the university has realized that the cost will be significantly higher for those lines that were routed underneath buildings.  You must now compute the length of lines under the buildings.  To do so, use the Geoprocessing Wizard (under the Tools menu).  Intersect two layers, your pipes (as input) and your buildings (as the overlay).  Save (and display) the result.  What is the total length of the lines that exist under the buildings?  What is the total length of the lines that exist not under buildings?  This last quantity is probably most easily computed by hand (as it involves only one subtraction regardless of the dataset size), but how might you get ArcMap to compute it?

  4. An independent problem.  Using the techniques illustrated so far in this lab, answer the question, "What percentage of the main campus is covered by parking lots?"  Your answer should obviously include a number, but should also include a description of the methodology by which you determined this.  Save all of the layers that you create in the process of answering this.  Note that you are permitted to do computations by hand if they are "one time regardless of data set size" as with the subtraction in Step 4.

  5. Nearest neighbors.  Close the pipes layers and open your fire hydrants.  Make sure that you have at least six hydrants in your layer.  (Add some if you do not.)  We wish to solve a problem similar to the "nearest dorm on fire" problem from Lab 5.  In particular, we wish to know what the nearest fire hydrant is for each of the buildings on campus.  To do so, we must create a spatial join.  Right-click the buildings layer in the table of contents and then join it with another layer.  Choose to "Join data from another layer based upon spatial location", the Hydrants layer and the second radio button, i.e. the one that selects nearest neighbors.  Having done so, determine the hydrant nearest Hopkins Hall.  Which one is it, and how did you determine that in the end?

    In a similar vein, describe how you would determine which points fell within given polygons.  What might be an application that would require such information?


  6. Buffer zones.  Another neat "computed" geometric feature is the use of buffer zones.  Using the Buffer Wizard (under the Tools menu) create a two-layer buffer zone around Hopkins Hall.  What might be the use of this feature?


 

To Hand In

  1. Display.  Adjust any symbology and ordering so that all of the layers you have developed today may be printed.  Print a monochrome copy of the layers on the lab printer.  (If necessary, two or more different printouts may be generated.)  
    2.  
  2. Submission.  Turn in the printouts, a write-up of the answers to the questions posed in lab, and a cover page.  

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.