Are you really done with your paper?
If yes, please continue with the fun. If no, click here.
One more visualization technique
Another way to visualize your surface data is to combine the hillshading with the colored elevation classification.
Try this:
Turn off the Contour layer for now
Arrange the layers in the TOC so that the quad4dem layer is on top of the hillshade layer
Open the Layer Properties dialog for the quad4dem layer
Select the Display tab
Change the Transparency value to 50%
Press OK
The values from the hillshade are now combined with the elevation colors to produce an interesting visual effect.
Try it again, but make the Transparency 80%
What happened? Try some other values.
When you have had enough visualization, try some analysis.
An advantage of the raster data model is it facilitates calculating properties of surfaces. One important property that can be derived from an elevation surface is slope. Slope is the rate of change in elevation at a surface location. When applying this property to a DEM it gives us an indication of the steepness of the topography.
By way of example, let's run a "quick and dirty" analysis of slope to identify areas of potential landslide vulnerability. Assume that for the soil characteristics in the Quad4dem, slopes greater than 35 degrees are "vulnerable" to landslides. Follow the steps below to calculate a slope layer and identify the areas with slopes greater than 35 degrees.
The new layer shows the slope for each cell in the Quad4dem based upon the elevations of the surrounding cells. According to the legend, the redder the color, the steeper the slope.
To visually identify slopes greater than 35 degrees you could use the legend editor and make two classes, one greater than 35 degrees, and one less than 35 degrees.
Instead, let's use the Raster Calculator function of the Spatial Analyst extension.
In the Spatial Analyst Tools under Map Algebra, double-click to run the Raster Calculator
Build an expression that says:
"Slope" > 35Make the output raster = c:\temp\slope35
Click OK.
What you should see are the grid cells that satisfy the logical expression you entered into the Raster Calculator dialog box.
Can you calculate the percentage of the Quad4dem that is susceptible to landslides?
Hint: Try examining the attribute table of the slope35 layer.
Question: Could you have calculated the percentage of area susceptible to landslides without using the Raster Calculator function?
3D visualization
Since we have 3 dimensions worth of information about the area covered by the Quad4dem, we should try viewing it in a 3-dimensional perspective. We do this in ArcGIS by using another extension called 3D Analyst.
To load the 3D Analyst, select Extensions under the Customize menu and put a check mark by 3D Analyst.
Now, Press the ArcScene button on the 3D Analyst toolbar to open a 3D viewer and 3D Scene Table of Contents
Not very impressive, is it?
Try this:
Open the quad4dem layer properties dialog
Select the Base Heights tab
Look better? Give it a spin. Zoom in.
I know it is tempting to explore a little further, but don't you have final projects to work on?
OK, so you can't get enough 3-D? Try it again in ArcGlobe. You will need to define the projection for the Quad4dem as: UTM NAD83 Zone 11.
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And if you still haven't had enough fun with rasters, try some or all of the above with the snippet of the National Elevation Dataset (NED) that is included in the project folder. To use it, you will need to do the following:
NED and many other layers are distributed through The National Map.
Exciting!
Last modified 11/16/2021