EXERCISE 6
GIS ANALYSIS: ATTRIBUTE MANIPULATION
FOR/GGR 525

BE SURE TO SAVE YOUR WORK REGULARLY!!!

  When editing a layer in ArcMap, make sure you use the Save Edits option on the Editor toolbar to save edits as a separate process from saving your map.

INTRODUCTION

The purpose of this exercise is to introduce the student to some GIS analysis that can be done through attribute manipulation within a single coverage. This is often the first step to any spatial analysis.

INSTRUCTIONS FOR COMPLETING THE EXERCISE

Step 1: Log-on to a computer, start ArcCatalog, navigate to your tutorial folder and delete all coverages there except your digitized coverage (fwsenet) and your most recent edited/built coverage (e.g., fwseneted).
We will need the space later and it never hurts to clean up your workspace every now and then.

Step 2: Copy the streams coverage into your directory using ArcCatalog.

  1. Use Connect to Folder in ArcCatalog to connect to the flag24 dataset on Spruce. See Exercise 1 for help on connecting to the dataset.
  2. Double-click the cover folder.
  3. Drag and drop the streams coverage from the flag24 dataset to your tutorial folder. You might have to copy and paste the coverage.  You will also have to remove the read-only attribute from anything you move over from the flag24 dataset.  Right mouse-click on the folder in which you put the coverage, choose Properties, and uncheck the "Attributes" box.  Apply the change.  
  4. Right mouse-click the streams coverage in your tutorial folder .
  5. Choose Properties.


  6. Click the General tab. This tab provides information about the coverage concerning the existing features and topology, for example that the coverage contains arc and tic features.
Step 3: Inspect the datafiles.
  1. Double-click the streams.dat table from the Table of Contents in ArcCatalog. The table should open. Inspect it.

  2. Click the items tab and inspect the table definition.
  3. Click OK.
  4. Now, look at the data in the table by clicking the Preview tab in ArcCatalog.


  5. Double-click the arc feature class from the Contents tab window. The attribute table definition should open. Inspect it


  6. Now look at the data in the table by clicking the Preview tab in ArcCatalog and then choosing Table from the Preview: dropdown (at the bottom of the Preview window).

Step 4: Change the order of the records (sort) based upon the appropriate attribute's value (in this case length).

  1. Open ArcMap.
  2. Add streams arc to the map (add the one in your own space).
  3. Open the streams arc attribute table by right mouse-clicking it in the table of contents and choosing Open Attribute Table.


  4. Now, see how easy it is to sort a table by sorting it on length. Right mouse-click over the length field and choose Sort Ascending.


  Step 5: Create several sets of selected coverage features based upon attributes which meet the following criteria.

  1. Select all streams 200-400 meters long.
    1. Click the Options button at the lower right of the attribute table document.
    2. Choose Select By Attribute...


    3. Double-click "Length" in the left-hand column.
    4. Click the >= button, then type "200."
    5. Click the And button.
    6. Double-click "Length" in the left-hand column again.
    7. Click the <= button.
    8. Type "400."
    9. Be sure the Method says "Create a new selection."

    How many are selected?

    If you look at the bottom you should see that 68 out of 865 records are selected.

  2. Add all streams less than 200M to the selected set. First we need to find out which are washes by looking up the codes in "Dat" in a lookup table called streams.dat.
    1. Click the Add Layer button.
    2. Navigate to your tutorial folder.
    3. Scroll down until you see a table called streams.dat and add it to ArcMap.
    4. Right mouse-click streams.dat and choose Open. Look at the field called "Datname." Find "stream." The "Dat" code for "stream" is "1." Streams.dat can be referred to as a lookup table because it is used as a reference to 'look up' information about the original (in this case the attribute) table.


    5. Click the Attributes of streams arc table to activate it.
    6. Click the Options button at the lower right of the attribute table document.
    7. Choose Select By Attribute...


    8. Click the Clear button to clear out the previous query.
    9. Double-click "Length" in the left-hand column.
    10. Click the < button, then type 200.
    11. Click the And button.
    12. Double-click "Dat" in the left-hand column again.
    13. Click the = button.
    14. Click in the far right window - or type- "1."
    15. Be sure Select Procedure says "Add to current selection."


    16. The selected set should now be greater (111 instead of 68) because we added to the current selection.
    17. Quit ArcMap after saving the map if you wish.

    3.  

Step 6: Add a new item (attribute) to the features attribute table called "class" in ArcCatalog and re-initiate ArcMap.

  1. Add a new item to the AAT file.
    1. Start ArcCatalog, or refresh if ArcCatalog is already open.
    2. Right mouse-click streams arc.
    3. Choose Properties.
    4. Click the Items tab.
    5. Click Add. This opens the dialog for adding items to the attribute table.
    6. In Item Name type "CLASS."
    7. For Type choose "Binary."
    8. For Width choose "2."

       

    9. If you typed anything incorrectly, click the Edit button and change the definitions.
    10. Re-initiateArcMap.
Step 7: Assign values for the new item (attribute) called CLASS.
  1. Right mouse-click streams arc and choose Open Attribute Table.
  2. Scroll to the right until you see the item "CLASS."
  3. Scroll up and down to see that all record values for "CLASS" are 0.

    Notice CLASS=0 for all records.

  4. Repeat the query above for finding all streams of length less than 200 m.

  5. Your selected set of data are less than 200 meters (the "selected set"). Assign the value "10" to the item "CLASS."
    1. Since you will be assigning data to the "CLASS" field or item, right mouse-click the field at the top on the field name.
    2. From the Editor toolbar, choose the Editor pulldown  .
    3. Click Start Editing.
    4. Choose Freeze/Unfreeze Column by right clicking on the "CLASS" field.


    5. Right mouse-click the "CLASS" field again and choose Calculate Values.
    6. Notice that the field for which you are calculating values ("CLASS") already appears in the Field Calculator window.
    7. Type "10" in the window.


  6. Select the appropriate streams for "CLASS = 20" and "CLASS = 30" and assign the values.
    1. Perform a new query to select streams greater than or equal to 200 m and less than or equal to 500 m.
    2. Use the Field Calculator to make the "CLASS" value for these streams equal to 20.
    3. Save your edits at this time.
    4. Perform a new query to select streams greater than or equal to 500 m.
    5. Use the Field Calculator to make the "CLASS" value for these streams equal to 30. If you are asked if it's okay to remove redo/undo information for calculating many records, answer Yes. This saves space and time by not saving your edit session, but makes it so that you are unable to use Undo/redo for this process.


  7. Scroll through the table to verify the results.  Make a layout showing the selected streams, and turn it in to your TA.  
  8. Save your edits and exit ArcMap.

     

    In the next exercise we will continue with another GIS analysis technique - creating buffer zones and corridors.
Return Return to Class Home Page...