G 424/524 GIS for the Natural Sciences
D. Percy
e-mail: percyd@pdx.edu

Assignment 3

Finding, downloading, clipping, and reprojecting data

Due: Thursday Feb 4

Now you actually go get some data, clip it and re-project it! You will also create your first GIS data, the study area. We will explore more data creation tools later in the term.

1. Download the lower resolution (1:250,000) vegetation from Oregon GIS Center, unzip it to a folder for assignment 3. Also get an airphoto and a topo map (PSU is in 122-45-E6)

2. Add this data to a new data frame. Put a copy of your landslides in this same data frame. The vegetation data set is in the State Plane custom projection, so in order to do any spatial analysis you need to either project your data (landslides and counties) to this coordinate system, OR project these data to Decimal Degrees. (You can get away with "on-the-fly" projection, but it's important to be comfortable with "physical" reprojection). Let's do the latter (Step 3), as it also demonstrates a useful geoprocessing function!

3. Create a polygon to clip out the vegetation you need, then project just that data subset to decimal degrees. This is an important tool in your arsenal.

• Open ArcCatalog, right-click in your assignment 3 folder, select New->Shapefile, set type to Polygon, Edit (coodinate system), Import, Choose vegetation.shp (this is a nice trick to get stuff into the same coordinate system).
• Back in Arcmap add your new shapefile, turn on the Editor (right-click the gray bar and choose Editor), make sure Target is set to your clip shapefile (not newgeol!!!), use the Polygon Tool to create a clip area (click, click, click, double-click), save edits and stop editting.

4. Use the ArcToolbox to Clip one layer based on another (Analysis->Extract->Clip). Keep track of where the new clipped coverage goes and what it's called!

5. Use the Toolbox to project this clipped data to DD.

ArcToolbox->Data Management Tools->Projections and Transformations->Features->Project
Will get you to a screen similar to the following, fill in the values like so, using your own data file names (vegetation_clip, instead of new_geology_clip) and use GCS_Nad83 (import from landslides or new_geology):

Insert a new data frame and put the projected data there. Create a layout showing both versions side-by-side. Comment on the difference...

6. If there is any documentation (metadata) associated with coverages you download, be sure to save it along with the data.

Part 2.

7. Go to http://seamless.usgs.gov and use the download tool to acquire some 1" and 1/3" NED in your study area. Get some tiles for a smallish area that has landslides (west hills?) Save them to your C:\temp.

Unzip them. Use the Mosaic To New Raster tool (ArcToolbox->Data Management->Raster->Raster Dataset) to "mosaic them". There is one band. Search Help for other mosaic'ing options.

Use ArcToolbox->Data Management Tools->Projections and Transformations->Raster->Project to reproject it to UTM zone 10 Nad 83 (must be in planar coordinates to do Surface Analysis), make sure you set your output cellsize to 30m, use Bilinear for the resampling method.

Load Spatial Analyst (Customize->Extensions)

Use ArcToolbox->Spatial Analyst Tools->Surface->Hillshade (accept the defaults) to make a hillshade of it. Put your landslides on it and the vegatation (try turning on Effects and make vegetation 50% transparent) and admire your pretty map.

Export a PNG of your map to include in your report and then walk away, assuming that the data on the C: drive will be gone when you get back next week.

More: create a slope map (Slope tool is near the Hillshade tool) from your UTM-projected data. Create a contour map (Contour tool found in same place as the others) from your DEM. Create a layout that shows elevation by displaying contours, slope by the default symbolization, and vegetation at 50% transparency. This is a second map for part 2.

For the writeup:

A brief introduction and overview of the assignment

Include the side-by-side layout from step 5 and comments.

Include the exported maps from step 7 and brief description of procedure to produce them.

Answer these questions from the readings:

Describe the difference between a tangent and secant projection. How many intersections does each have with the theoretical shape of the earth? (Johnson)

What is the difference between "reality", the "Data Model of Reality" and a "Computer Oriented Data Model" (Rasmussen).

Give an example (from an area you are interested in) where the "ideal" data model might differ from the DBMS/GIS implementation. What sacrifices are you willing to make? How will this affect querying the data?