Lab Practical Final Review

Lab Practical Final Review This short exercise will review most of the concepts that will be covered on the lab final. The lab final is cumulative, but more emphasis will be placed on the raster related operations that you have learned since the mid-term. Here are some of the vector related topics that may be covered: - Buffers - Selecting by Location or Attribute - Creating a New Shapefile - Projections - Editing If you need to review some of these concepts, refer to your “Vector Review” packet. If you have lost it, e-mail me so I can get you another copy. In the last exam, I provided you with all of the data you needed to perform your tasks. This time, however, I will require you to use the TNRIS website (www.tnris.org) to get some of the data you need for the exam, during the exam. There is a powerpoint in the Inro_GIS folder named “Using TNRIS”. Review it, and follow along with it to figure out how to use it. If you have any questions, do not be afraid to e-mail me. All the data you will need for this review is in the folder “Final_Review” in the Intro_GIS folder. Copy it to your personal folder to begin. Mosaic Mosaic is an operation that takes two or more DEMs and lines up the elevation so that they form one continuous raster. We will use Waco East and Waco West Quadrangles in this example. 1. Start ArcMap and add WacoE and WacoW to the view. The two rasters do not line up. The mosaic tool will fix this.

Now, there are two different ways to mosaic a raster. Both are in ArcToolbox. The ‘Mosaic’ tool requires you to select one raster and will mosaic all other rasters to line up to that one. ‘Mosaic to new raster’ will do just that, it will create a new raster in the process. I prefer to use ‘mosaic to new raster’ because the other tool will permanently change the other raster, and I like to keep my original datasets intact. 2. Click on “Mosaic to new raster” The following dialog will appear: Simply input your two rasters in the first box. The next one is trickier. You MUST select a folder the new raster to go in. Then, simply name it and hit OK. Now, the two rasters have become one continuous DEM. (As a side note, sometimes when you mosaic DEMs, there is some blank space in the middle. This comes from projection problems and is usually fixed with a process taught in advanced GIS… so don’t worry about it)

Hillshade This tool simulates the sun shining down upon the raster. Use the hillshade tool on the new mosaic raster with azimuth of 45 and an altitude of 50.

Extract By Mask The extract by mask tool works similar to the “clip” tool you used back in the first half of the semester. The difference here is that you will be using it to clip a raster. 1. Add the “example_mask” layer to the data frame. This shapefile will be used to clip the raster. 2. Open the “Extract by Mask” tool in ArcToolbox. The following dialogue will appear:

The input raster is the raster that you are going to clip, the mask data is the ‘cookie cutter’ that you are using to clip the data, and the output will look like this:

Interpolation Methods You have done several interpolations over the last few weeks, and you should know how to do this by now. In the folder is a dataset called “UpperLevel”. It is point data for water levels in an aquifer classified by the field “ulv”. Use IDW to interpolate it, then check your result against mine below:

Remember, the second line, ‘Z value field’ needs to be the field with the data you want to interpolate. Sometimes, the computer automatically changes this to “id” so you need to change it to “ulv”.

Raster Calculator This tool is located on the spatial analyst toolbar. Click this button to get the calculator. The raster calculator can be used to convert rasters from feet to meters and vice versa. Pull up the raster calculator, and divide the new IDW raster by 3.28. The rater essentially remains the same, but the units , which were in feet, are now in meters.

Reclassify Data This tool is also under the spatial analyst toolbar. You can use this tool to create a new rater with different values. Use the new raster that you just created with the raster calculator. Reclassify it so that elevations of 168.969 – 170 become 1, 170 – 172 becomes 2 and 172 – 173.814 becomes 3. It will look like this:

Hopefully, this review has been helpful. If you have any questions, please ask me now, as I will be unable to answer any e-mails over Thanksgiving until Sunday.