Saturday, November 04, 2006

Essentials of Environmental Science - GIS Lab
Spatial Analysis of Casperkill Data

In this lab we’ll perform some of the analytical steps you can use to understand the distribution of stream quality parameters, or of risk factors that influence a stream.

The directions in this lab are somewhat terse, in part because I think much of the methods involved are communicated easiest verbally, and in part because it takes a lot of precious time to read directions in the current context. Please do your best to remain flexible, and if you find yourself becoming frustrated with the software, consult with your neighbors and the instructors to sort out a solution. Often we learn a great deal by making mistakes.

We will practice importing points, changing symbols, buffering and clipping, and basic map design as a group. Then you will have time to work on your own. We’ll try to include some show-and-tell to display your work to the group.

Taking notes: it’s hard to pause for note-taking, but it’s a good idea! You will not remember the steps taken today if you don’t take notes. I strongly recommend note taking!

Here is where you’ll find the tools you need:

Symbology: change the colors, sizes, grouping, and so on for point, line, or polygon features by opening the Properties window (double-click or right-click on the layer name), then click on the Symbology tab

Buffer tool: in the Toolbox (click on the red toolbox button to open it), search for the Buffer tool. (normally, use Dissolve Type: ALL)

Clip, Dissolve, and Calculate area are also in the Toolbox (search by name)
Select features by their location in a buffer: under the Selection menu (top of the ArcMap window), find Select by Location.

To examine attributes of selected features: open the attribute table of the layer: right-click on the name of the layer. You can then use Statistics to calculate mean, min, max, and histogram.

Screen capture windows (to paste in a word document): Alt-print screen copies the active window, such as a histogram report. Ctrl-V to paste in a word document.

Possible tasks: (we may not accomplish all of these)
Plot the Casperkill sample sites as points (“events”), using their coordinate locations.
Display the points using point symbols graduated to express data values.

Buffer the stream (at 50, 100, 500, 1000 m).
Clip digitized land use by the buffered area, then calculate area of different classes of land use.

Create a new point shapefile and identify risk factors to the stream, and show those risk factors to the class.

Assignment: Turn in the following next week.
Produce a map (without air photos, but with a legend and scale bar) showing your findings from some (probably not all) of the work above. Write a 1-2 page analysis that explains what you can interpret from what you see in the map. You will be graded on the thoughtfulness of your writing, not on the depth of your GIS work. Your GIS analysis may be very simple, but try to think thoroughly about the evidence you have, the questions it raises, and the information that can be found in it about environmental factors affecting the stream.
As you write, practice writing cleanly and accurately. Stick close to the map and avoid sweeping generalizations, sloppy grammar, and other careless habits. Any figures or tables appended to your written work should have captions, and you should clearly explain what each figure or table shows and what the reader is to learn from it.

digitized data values:
1 = trees
2 = neighborhoods
3 = parking lots
4 = mowed grass
5 = open water
90 = roads

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