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Exercise #2 — Maps As Data (MapCalc)
GIS Modeling, GEOG 3110, University of Denver
Team Members: __________
Date: ___________
Part 1. Understanding Basic Concepts and Terms
Question 1. Based on the lecture and readings briefly define and discuss the following concepts
surrounding “the level of detail” in mapped data—
Map Scale— Insert your answer…
Spatial Resolution— Insert your answer…
Thematic Resolution— Insert your answer…
Minimum Mapping Resolution— Insert your answer…
Temporal Resolution— Insert your answer…
Comment on how mismatched scale/resolution in a set of maps can affect GIS analysis and modeling.
Insert your answer…
Question 2. Based on the lecture and readings briefly define and discuss the following map data types.
Be sure your definitions include discussion of which terms refer to the numeric distribution and which refer to the geographic distribution of mapped data.
Nominal — Insert your answer…
Ordinal — Insert your answer…
Interval — Insert your answer…
Ratio — Insert your answer…
Binary — Insert your answer…
Choropleth — Insert your answer…
Isopleth — Insert your answer…
Access the MapCalc system using the Tutor25.rgs database.
Screen grab and insert below a 3-D lattice display of the Slope map.
Insert figure (don’t forget to include a Figure Number, a Caption and to Reference/discuss the figure in the text of
your answer)…
What is the Data Type of the Slope map? ...what is its Display Type ?…what is its Display Form? —
Insert your answer…
What is the interpretation of a terrain steepness of 0%? Insert your answer…
Is a location with a 20% slope twice as steep as a location with 10% slope? Insert your answer…
Why are there no negative slope values? Insert your answer…
Screen grab and insert below a 2-D grid display of the Districts map.
Insert figure (don’t forget to include a Figure Number, a Caption and to Reference/discuss the figure in the text of
your answer)…
What is the Data Type of the Districts map? ...what is its Display Type ?…what is its Display Form? —
Insert your answer…
Could you calculate a slope map from the Districts map? Insert your answer…
What, if any, would be the interpretation of its slope values? Insert your answer…
Part 2. Characterizing Geographic Space …Discrete versus Continuous
Access the MapCalc system using the Tutor25.rgs database and display a 2-D lattice contour plot of the Elevation map.
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 lattice (wireframe) plot of the map surface. Click on the Shading Manager icon ( c ) to pop-up the thematic mapping window.
<insert “Ranges 5” display> <insert “Ranges 7” display>
Describe the differences in the two plots and discuss their impacts on the thematic display of the continuous surface data.
Insert your answer…
Part 3. GIS Modeling… Simple Erosion Model
Access the MapCalc system using the Tutor25.rgs database and on the Main Toolbar, click on the Grid Analysis icon, and use the map analysis tools to complete the following series of commands.
Click on the Slope icon (under the Neighbors button ) and specify…
Map Analysis Neighbors Slope
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.
Note that the default map display for the Slope command is continuous data type.
Click on the Renumber icon (under the Reclassify button ) and specify…
Map Analysis Reclassify Renumber
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 to add it to the list.
Note that the default map display for the Renumber command is discrete data type.
In displaying maps, be sure to set the most appropriate 2D or 3D display form, Grid or Lattice display type and Discrete or Continuous data type for a proper display of the data (not always the default display).
Click on the Drain icon (under the Distance button ) and specify…
Map Analysis Distance Drain
DRAIN Entire OVER Elevation FOR Flowmap
Note that the default map display for the Drain command is continuous data type.
Click on the Renumber icon (under the Reclassify button ) and specify…
Map Analysis Reclassify Renumber
RENUMBER Flowmap ASSIGNING 10 TO 1 THRU 10 ASSIGNING 20 TO 10 THRU 20 ASSIGNING 30 TO 20 THRU 1000 FOR Flow_classes
Click on the Compute icon (under the Overlay button ) and specify…
Map Analysis Overlay Compute
Figure 5-1. 2D Grid Display of the Elevation Map (input).
Figure 5-2. 2D Lattice Display of the Slopemap (output).
Note: Be sure your answer includes a short discussion of what is happening in the processing step. Be sure to reference the embedded figures and identify the display and data types of the maps, such as…
Figure 5-1 is a 2D grid display of the Elevation data (Base Map; figure 5-1) containing ratio data from 500 to 2500 feet. The terrain data is analyzed using the Slope command to create a Slopemap (Derived Map; figure 5-2) containing ratio data from 0% slope (flat) to 65% (steep). Note that the steepest terrain is located in the north-central portion of the project area (green tones).
Slope values for each cell are calculated using the eight neighbor cells, that is, a 3x3 window is used for each calculation. The value is applied as a percent, to the centroid of the center cell. The default procedure aligns a best-fitted plane to the values in the window, and assigns the slope of the plane to the center cell. The window then shifts over one cell and the process repeats. Other options use the maximum, minimum or average of the eight individual slopes in the slope window.
Now on your own , repeat the descriptions for the other four Steps of the simple erosion model.
Step 2 Insert your answer in a similar fashion as the example for this step…
Step 3 Insert your answer in a similar fashion as the example for this step…
Step 4 Insert your answer in a similar fashion as the example for this step…
Step 5 Insert your answer in a similar fashion as the example for this step…
Question 6. Considering the combined categories of “Heavy_flow and Steep_terrain”, “Heavy_flow and Moderate_terrain” and “Moderate_flow and Steep_terrain on the Erosion_Classes map you just created, use the Shading Manager to graphically identify these areas of significant erosion potential as Red and all other locations of lesser erosion potential as Light Gray. Embed a screen grab of your map below.
Insert figure…
How many acres and proportion of the total study area falls under the significant erosion potential class (color= red)?
Insert your answer…
Use the sequence Map Analysis Reclassify Renumber to generate a map called High_erosion that
isolates the areas of significant erosion potential with the new value of 1 assigned to areas with significant erosion potential (as noted above) and new value of 0 assigned to all other areas. Embed a screen grab of your map below.
Insert figure…
How many acres and proportion of the total study area falls under the significant erosion potential class (value= 1)? Where do they mostly occur?
Insert your answer…
Describe the “significant difference” between the Graphic (Shading Manager) and Numeric (Renumber) versions of the areas of high erosion potential.
Note : Submit Optional question answers as separate Word document files with the Question number and your name (e.g., Optional_2-1_yourName.doc)… do not include them with the normal weekly lab reports.
Optional Question 2-1 (extra credit= 3 points possible; complete individually and submit your answer as a separate email). Based on class discussion and your experience viewing the data structures/formats for MapCalc, Surfer and ESRI Grid describe the similarities/differences and advantages/disadvantages among the three approaches to storing grid-based mapped data. Use the Slope map in the Tutor25.rgs database (MapCalc_Tutor25_rgs.txt, SLOPE_Tutor25_Surfer_grd.txt and SLOPE_Tutor25_Esri_asc.txt in the …\MapCalc Data\Misc folder) for illustration and discussion similar to the slide set presentation used in class to describe the data structure/format of the Elevation map.
Insert your discussion with figures then email as separate file…
Optional Question 2-2 (extra credit= 3 points possible; complete individually and submit your answer as a separate email). Based on the class discussion and assigned, optional and other readings you may find, write a short essay (less than 750 words) discussing the differences in assumptions, approaches,
…and the ArcGIS Help (Spatial Analyst) in the GIS lab to complete the translation table below for the basic Campground Suitability Model you completed in Exercise #1. Be sure your answer addresses any disparities in the commands.
MapCalc Command
Processing Achieved …what information is derived
Esri Grid Command SLOPE Elevation…
Creates a map of terrain steepness expressed in percent inclination; input is a base map of Elevation; Esri SLOPE provides an option for output values to be in degrees as well as percent
SLOPE
SPREAD Roads… SPREAD Water… RADIATE Water… ORIENT Elevation… RENUMBER Slopemap… RENUMBER Proximity_roads… RENUMBER Proximity_water… RENUMBER Exposure_water… RENUMBER Aspectmap… ANALYZE S_pref… Calculates a weighted average of a “stack” of map layers; input is the set of derived campground preference layers calibrated from 1= least preferred through 9= most preferred; Esri WEIGHTED OVERLAY requires building a separate weighted overlay table
WEIGHTED
OVERLAY
RENUMBER
Proximity_water… RENUMBER
Slopemap…
COMPUTE N0_slope…
COMPUTE Constraints…
