Exercise #2 — Spatial Analysis Operations

Introduction to GIS Modeling, GEOG 3160, University of Denver, Spring 2001

Name _____<enter your name>_____

Date _____<enter date>______

MapCalc Manual, Tutorials

Part 1. Capturing and Embedding Screen Images (SnagIt)

Access SnagIt by double-clicking on the icon on your desktop or Startà Programsà SnagItà SnagIt 5.

Set the Input and Output parameters by…

ü From the Main Menu select Input and check the “Window” item.

ü From the Main Menu select Output and check “File” and “Preview Window” items.SnagIt Select the “Properties” items and set as shown below (.GIF, SNAG-, 4, C:\Temp), then press OK.

ü Minimize the SnagIt window

Access MapCalc by double-clicking on the icon on your desktop and specifying the TUTOR25 database.

Use the following procedures to generate lattice and grid 3-D displays of the Elevation map…

ü From the Main Menu select Windowà Elevation

ü Press the 3-D Toggle view button to display the elevation surface as a 3-D plot

ü Press the Layer Mesh button to superimpose the grid lines on the plot

ü Press the Use cells button to toggle between lattice and grid displays of the elevation data

Capture screen images of both the Lattice and Grid displays by…

ü Simultaneously pressing the keys Ctrl/Shift/P.

ü Move the cursor so it is centered on the map display and that portion of the screen is outlined in red.

ü Click the mouse and press the green arrow in the pop-up window to save the captured image.

ü Press the Use cells button to toggle to the other display type and repeat the three steps above to capture it.

Access Microsoft Word and open the C:\Temp\Exer2.doc file (previously downloaded from the course web site). Use the following procedure to embed the screen grabs into this document…

ü Place the cursor below the “Question 1. …” subheading below.

ü From Word’s Main Menu select Insert, click on “Picture” and navigate to C:\Temp\SNAG-001.gif and double-click on the file.

ü Right-click on the picture, select Format Picture and specify the Size width as 2.5 inches.

ü Press the Space bar to position the cursor a couple of spaces to the right of the picture and enter “Figure 1. Lattice display of the elevation surface.”

ü Repeat the above procedure to embed the other screen grab (C:\Temp\SNAG-001.gif).

Question 1. Insert the “screen grabs” below and label them as directed in the instructions above.

(Optional 2-1… 5points). Create your own “User’s Guide” that illustrates the following SnagIt optional settings and picture formatting options in Word (embed screen captures from MapCalc with captions as appropriate)…

SnagIt Input Settings

ü Screen—

ü Window—

ü Active Window—

ü Region—

ü Fixed Region—

SnagIt Output Settings

ü Printer—

ü Clipboard—

ü File—

Picture Format Settings (in MS Word)

ü Colors and Lines—

ü Size—

ü Layout—

ü Picture—

In preparing your guide you should use SnagIt’s and Word’s online manuals for help in developing your discussion and embedded MapCalc displays for illustration.

Part 2. Understanding Basic Concepts and Terms

Question 2. Based on the lecture and readings briefly define and discuss the following concepts surrounding “the level of detail” in mapped data— 1) Map Scale, 2) Spatial Resolution, 3) Thematic Resolution, 4) Minimum Mapping Resolution and 5) Temporal Resolution. Comment on how mismatched scale/resolution can affect GIS analysis and modeling.

Question 3. Based on the lecture and readings briefly define and discuss the following map data types— 1) Nominal, 2) Ordinal, 3) Interval, 4) Ratio, 5) Binary, 6) Choropleth, and 7) Isopleth. Why is a knowledge of data type so important in GIS modeling? Could you calculate a slope map from a base map containing ordinal data? What, if any, would be the interpretation of the slope values?

Part 3. Characterizing Geographic Space… Discrete versus Continuous

Access the MapCalc system and display a 2-D contour plot of the Tutor25 elevation data.

MapCalc Tools

Click on the Layer Mesh icon (a) to superimpose the 25x25 analysis grid.

Click on the Toggle 3-D View icon (b) to get a wireframe plot of the map surface.

Click on the Shading Manager icon (c) to pop-up the thematic mapping window.

Shading Manager

Note the current settings. What is the…

“Calculation Mode for Ranges” setting? ___________

“Number of Ranges” setting? ____________

Assign the settings to Mode= Equal Ranges and Ranges= 10. Note the changes in pattern of the colored zones, then press OK.

Click on the Rotate icon (d) then click and drag the plot to rotate the display.

Click on the Zoom In/Out buttons (e) to rescale the plot.

Click on the Reset View to Defaults icon (f) to return the plot to its standard form.

Click on the Use Cells icon (g) to view the surface as an extruded plot.

Change the settings to Mode= Equal Count and Ranges= 10. Note the changes in pattern of the colored zones, then press OK.

Change the settings to Mode= +/- 1 Standard Deviation and Ranges= 10. Note the changes in pattern of the colored zones, then press OK.

Homework Question 4. Prepare a brief write-up (including screen grabs) of the “Thematic Mapping” processing you just completed. Include discussion of the Data Ranges and Cell Membership as reported in the Shading Manager table for each of the three categorizations (Equal Ranges, Equal Count and +/- 1 Standard Deviation).

Which of the three do you think “best represents” the map surface? Explain your reasoning.

Homework Question 5. Repeat the process for your favorite method (Equal ranges, Equal Count or +/- 1 Standard Deviation) using half the number of intervals; Ranges= 5). Describe the effects and discuss their impacts on the thematic display of the data.

Homework Question 6. Comment on whether you think the “method of categorization” (Mode) or the “number of intervals” (Ranges) has the greatest affect on changing the patterns of the colored zones. Your discussion ought to include your thoughts on how representation of map surfaces (continuous) as polygon zones (discrete) could lead to different interpretations/conclusions of the same set of mapped data.

Part 4. GIS Modeling… Simple Erosion Model

Access the MapCalc system using the TUTOR25 database. On the Main Toolbar, click on the Grid Analysis icon , then use the analysis tools to complete the following macro…

Click on the Slope icon (under the Neighbors button) and specify

SLOPE Elevation Fitted FOR Slopemap

Note that the slope values form a gradient from 0% (flat) to 65% (steep) that is automatically “categorized” into seven intervals with colors “ramped” from Red to Yellow to Green.

Click on the Renumber icon (under the Reclassify button) and specify

RENUMBER Slopemap ASSIGNING 1 TO 0 THRU 10 ASSIGNING 2 TO 10 THRU 30 ASSIGNING 3 TO 30 THRU 1000 FOR Slope_Classes

…by individually entering the “assigning” phrases (ASSIGNING <New Value> TO <Old value> THRU <Old UpperValue>) and pressing the “Add” button after each phrase is complete.

Note that the default map display is a bit confusing as it is attempting to show the data as continuous (7 intervals from 1 to 3). To get a more realistic map of the “categorical” data, press the “Use Cells” (switch from lattice to grid display type) and “Data Type” (switch from continuous to discrete data type) buttons on the main toolbar.

Click on the Drain icon (under the Distance button) and specify

DRAIN Entire OVER Elevation FOR Flowmap

Click on the Renumber icon (under the Reclassify button) and specify

RENUMBER Flowmap ASSIGNING 10 TO 1 THRU 10 ASSIGNING 20 TO 10 THRU 20 ASSIGNING 30 TO 20 THRU 1000 FOR Flow_classes

Remember to switch to “grid” display type and “discrete” data type for a proper display of categorical data.

Click on the Compute icon (under the Overlay button) and specify

COMPUTE Flow_classes Plus Slope_classes FOR Erosion_codes

Remember to switch to “grid” display type and “discrete” data type for a proper display of categorical data (2-digit code).

The following flowchart outlines the steps you just completed…

Homework Question 7. Identify and briefly describe the four fundamental classes of map analysis operations. Which classes do the operations Slope, Renumber, Drain and Compute belong?

In your own words, describe how these four operations work and characterize the maps they derived in the simple erosion model you completed.

Create a “narrative flowchart” with embedded maps displays that describes the five processing steps of the erosion model. Hint—Step 1 heading, input/output maps and text description of what is happening (repeat for the other four Steps).

Assuming Heavy/Steep, Heavy/Moderate and Moderate/Steep erosion classes identify areas of significant erosion potential, how many acres and proportion of the total study area falls under this classification?

Generate a map that isolates the areas of significant erosion potential.

Part 5. Calculating Landscape Metrics

Note: see http://www.innovativegis.com/products/fragstatsarc/manual/index.html, for an online version of the FragStats*Arc manual that discusses the concepts, procedures and metrics involved in landscape analysis. This reference will help you answer the optional questions (should you choose to tackle them).

(Optional 2-2… 5points). Prepare a short paper (3-5pages) summarizing the concepts, assumptions and considerations in applying landscape metrics to natural resources management. Your discussion should include the differences between Patch, Class and Landscape perspectives, as well as the importance of Extent and Grain.

(Optional 2-3… 5points). Do you believe current GIS vegetation maps are suitable for landscape analysis? Explain your position. Your answer should weigh the two opposing positions discussed in class…

ü Do we have the technological cart (can calculate metrics) in front of the scientific horse (now idea what they mean)?

ü Can we afford to postpone consideration of landscape structure in natural resource planning and management while science catches up to technology?

Suggest and briefly discuss a couple of other application areas where GIS technology might be ahead of scientific understanding.