Part 3—Download and Import DEM Data
Step 1 – Access GeoBrain Website and Practice Navigating around the Map
- Click on the link GeoBrain DEM Explorer. An interactive map will open in a new window.
- Practice moving around the Digital Elevation Model (DEM) Explorer Interface with the Zoom and Pan tools located on the left side of the toolbar (shown below). The tools are grouped by function: zoom tools are on the left, query tools in the middle, and selection tools are on the right side. The numbers on the right are latitude and longitude.
The GeoBrain DEM Explorer interactive map tool allows you to choose any location in the world using a manual selection tool or by specifying a pre-defined area from a list of options. You can pan and zoom using the navigation tools, and add or remove U.S. State and World Country boundaries using the overlay tools.
Begin by reading the guidelines provided in the "Welcome!" box. There are three basic steps to working with this interactive map interface. First, select your area of interest; second, select your data by name, format and output setting; third, perform analysis on the data and download the data to use in a GIS project. When you are done reading, close the "Welcome!" box.
- Click once on the Zoom In
button. The view zooms at the center of the map and displays Africa, with the countries labeled. While zooming, give the map several seconds to refresh/redraw.
- Click once on the Zoom Out button. The view returns to the previous zoom level.
- Click the Zoom In button once or twice. Use the Pan button to pan up, down, right, or left across the map.
- You can also use the Dragbox Zoom In tool to click and drag a defined location within the map that you want zoom in to.
- When you are done exploring click the Zoom to Full Map
Step 2 — Locate Oregon and Select an Area of Interest
- In the Map Layers sidebar, located on the right-hand side of the map, turn on the World Boundaries > Country and the USA Boundaries > State, by clicking in the appropriate check boxes.
- Click and drag around the Western United States with the Dragbox Zoom In tool. Continue zooming in until you have Oregon centered in your view. Be sure you can see the coastline.
- Practice making selections with the five types of tools provided in the DEM explorer interface (tools shown to the right). You can clear your selections by clicking the Clear Defined Area button on the toolbar. Active selections are highlighted in blue on the map.
- Use the Define Polygon Area or Define Rectangle Area selection tools to select an area of interest.
- Alternately, click the Define Area by State / County button on the toolbar. Use the drop-down menu to select the State of Oregon.
- When you are done exploring, click the Clear Defined Area button on the toolbar.
Step 3 — Load DEM for an Area of Interest to the Preview Window; Process, and Download the Data
- Once you have selected a region of interest. Click the Download Data for Defined Area button (it looks like a folder with a green arrow on it).
- In the download dialog box, first click the Data Name: STRM30_PLUS Elevation and
Bathymetry (Global) radio button (bottom one on the list), then select the Output: Format GeoTIFF and set the Projection to Lat /Lon. Finally, check the .zip box, and click Submit. You will get a message that your request is being processed.
- In the DEM Analysis window that opens you will see two toolbars at the top of the window: the Terrain Analysis and the Hydrologic Analysis. Below the toolbars, in the Data Preview window, you will see an image of the DEM that you have selected.
- Using the Terrain Analysis tools, select the Hillshade button. Change the Z-Factor to 10 in order to exaggerate the shading. Click Submit.
- In the Hill Shade Preview window, preview the image. When you are done, close the Hill Shade Preview window.
- Next, in the Terrain Analysis window, click the Contour button. Set the contour intervals to 5 meters and click Submit. In the Contour Preview window, preview and then download the shapefile. Save the shapefile to a location on your desktop or in your Documents folder, where you can easily locate it again. Close the Contour Preview window.
- You should now have a contour shapefile to add to your project.
- Click the Contour button.
- Set Interval (Unit: meter) to 5.
- In the Contour Preview window, click Download to download the files.
- You will be asked where you want to save the file; save it to your desktop or in your Documents folder. Note: depending on your browser, your file may be automatically downloaded to your Downloads folder and unzipped (unstuffed), in which case you just simply need to drag it to the desired locationideally, you can place this unzipped folder in the AEJEE data folder.
- Check that you have all four of these files properly downloaded and unzipped, and then close the DEM Explorer window. Move the entire folder of files into your AEJEE Data folder.
- In order for these files to work with AEJEE you must rename all 4 of the files with a shorter file name, "ORcoast_contour_5m". Leave the extensions as they are (.dbf,.shx,.shp,.prj, etc).
A digital elevation model (DEM) is a digital representation (raster image) of ground surface cartographic (topography or terrain) information. DEM data is collected in a number of ways. Most commonly, remote sensing satellites collect the data needed to prepare a DEM. In this case, the international Shuttle Radar Topography Mission (SRTM) collected the data in February 2000. The SRTM was a specially modified radar system that flew onboard the Space Shuttle Endeavour.
Hillshading is a shading method used to enhance or exaggerate topographic features in a topographic raster image, such as a DEM. By creating a 3-D effect, it gives the viewer an overall visual impression of the terrain. Contour lines are mathematically derived from the digital data recorded in the DEM image and therefore compliment the data in the image. Contour lines connect points of equal elevation and are readily analyzed in a GIS. They are also known as contour intervals.
Step 4 – Launch AEJEE, Add Data, and Edit Properties
- Launch AEJEE and open the project file that you saved in Part 2. When AEJEE launches, Oregon is centered in the view; only the U.S. States and Oregon Border are showing.
- Click the Add Data... button and locate the .shp file in the unzipped folder that you downloaded from the GeoBrain Web site or else use the one at the end of Step 3 (above). Single click to select the file, ORcoast_contour_5m.shp, and then click OK.
- AEJEE imports the shape file, and places it on the map.
- The new data layer should now be visible on the map and in the Layers List. Make it the Active layer and click the Zoom to Active Layer button in the toolbar.
- You will see that the layer includes data from the coast of Oregon.
- Make the new layer the active layer in the Layers List, right-click (ctrl-click on a Mac) and choose Properties... from the drop-down menu.
In the Properties window that opens change the following:
- Draw features using: Graduated Symbols
- Field: elevation (Hint: this process works best if you change this setting last.)
- Classes: 16
- Style: Solid Line
- Classified by: Equal Interval
- Color: Start Blue and End White
- Size: Start 1 and End 1
- Click Apply and then OK
- Use the Zoom to Active Layer button to zoom into the extent of this layer and use the Pan
tool to explore the topography of the Oregon coastal region. While exploring, consider the following questions:
The blue lines off the coast are bathymetric contours which are below sea level. The areas with the greatest elevation are away from the coast. The widely-spaced areas near the coast are close to sea level and flat. They include beaches and areas that might be inundated (flooded) by a tsunami wave.
- What do the blue lines off the coast of Oregon indicate?
- Where are the areas with the greatest elevation?
- Look for areas that have widely-spaced contour lines on the coast, what type of areas might these be? How might they be impacted by a tsunami wave?
- When you are done exploring, zoom the map back to the full extent of the Oregon coast.
In order to give the data more meaning, it is helpful to change the contour lines to be colored by their respective elevations. To do so you will need to edit the layer.
Step 5- Save Your Project File and Quit AEJEE
- Now that you have added the new data, choose File > Save As... and name your project Tsunami Runup_Part3, or some other unique name. Then click the Save button.
- Quit AEJEE.