Advanced Geospatial Analysis Skills: Review and Self-Assessment

Raster Analysis

In this step, you will download data from the USGS National Map viewer. Then you will use your raster analysis skills to answer the question below. Remember, raster analysis includes understanding the spatial resolution (cell size) of the data, using raster analysis tools, and performing mathematical computations on raster datasets.

Skill Drill: Acquire Elevation Data from the USGS National Map Viewer

In previous courses, you learned how to acquire data from public sources. Here you will download a digital elevation model from the USGS National Map Viewer. You will then use the digital elevation model to answer the question below. Navigate to the USGS National Map Viewer at https://viewer.nationalmap.gov/basic/. Click on the link to download GIS data. This link will take you to the map viewer. On the right, zoom in and center the map to the approximate region of interest. For this activity, zoom into Mount Shasta, California. On the left, under Elevation Products, check the box next to 1/3 arc-second DEM. Then click. Find Products.

An image of the National Map Viewer Find Products Page
To acquire data for a specific region, you must use the map to zoom to that location.

On the Products tab, you will see a list of datasets available for download. To determine which digital elevation models cover the area of interest, you can click on the Footprint link to see the boundary of the dataset. You may need to zoom out a little to see the entire footprint. At this time, only one digital elevation model covers the area of interest. Click the Download link to download. Save the file in your original folder and decompress it.

Check the spatial reference of the digital elevation model. Then, use the Project Raster tool to create a copy of the data with the NAD 83 UTM Zone 11N spatial reference. Save the Output Raster Dataset to your working folder. Under Output Coordinate System, choose NAD_1983_UTM_Zone_11N. When you are ready, click OK. In ArcMap, open a new blank map document add the layer to your Table of Contents. If asked to create pyramids, say Yes.

An image of the DEM loaded into ArcMap

In a separate document write down the answer to the following questions:

Questions 10: What was the original Spatial Reference System before the digital elevation model was projected?

Question 11: What is the total area (in square meters) of all the regions having a slope of equal to or less than 40 degrees?