GEOG250
STEVE WALKER'S --Introduction to grid-based data: Digital Elevation models and scanned USGS Maps
1. Preliminary Steps
1.1. Double-click on ‘My Computer’
1.2. Browse to C:\GisData and notice all the data and projects available here. We will be using the AV3_ Mt_Baker_AV3 data.
1.3. Browse to C:\TEMP folder and create your own new work folder
2. This is just an empty project, to which we will add data.
2.1. Start ArcView and add the Extensions -- Spatial Analysis and Spatial Tools
2.2 Now from the project manager Add a new View
2.3. From the View menu, select add theme, or use the ‘add theme’ button
2.4. When the add theme window opens, change the ‘data source type’ selection in the lower-left of the window to ‘Grid Data Source’
2.5. In C:/GISdata/AV3_ Mt_Baker_AV3 folder highlight ‘bakerelev’ and click ok. Now the Mount Baker elevation grid is added to your View. Each cell in this grid represents the elevation at that (10meter x 10 meter) point. It is displayed with a ‘graduated color’ legend, where the darker the color, the higher the elevation.
2.6. If you want to, you can open the grid’s legend by selecting ‘edit legend’ from the Theme menu. You can then select a color ramp such as ‘elevation#1’ to display the grid in a different set of colors.
3. Create a ‘shaded relief’ representation of your elevation grid.
3.1. The elevation grid should be active (ie highlighted/embossed). If not, click on its name to make it so.
3.2. From the ‘Surface’ Menu, choose ‘compute hillshade.’ You can leave the azimuth and elevation values where they are, then click OK.
3.3. The surface will appear as though a light were shining on it, creating highlights and shadows.
4. Create contours from the elevation surface.
4.1. Making sure the elevation grid is still active, return to the ‘Surface’ Menu, and click ‘create contours’
4.2. Set 100 as the contour interval. This will create contours every 100 meters (our elevation data is measured in meters.)
4.3. ArcView will determine where the 100 meter contours are located, and automatically create a shapefile theme containing these contours.
4.4. Turn these contours on and practice with adjusting their symbols, if you wish.
6. Add the Scanned USGS Quad Map
6.1. From the View menu, select add theme, or use the ‘add theme’ button
6.2. When the add theme window opens, change the ‘data source type’ selection in the lower-left of the window to ‘Grid Data Source’
6.3. From the C:/GISdata/AV3_ Mt_Baker_AV3 folder highlight ‘bakermap’ and click ok. The Mount Baker elevation grid is added to your View. If you do this step correctly, the map will appear in a set of random colors: it won’t really look like a USGS map. Zoom in on this map.
6.3.1. Ironically, if you do this step wrong, adding the map as an image, it will display correctly.
6.4. Double-click on the quad map’s legend in the Table of Contents.
6.5. The legend editor opens, click on ‘Load’ in the upper right hand corner of the legend editor window
6.6. A file browser window opens: choose ‘drg.avl’ in this window and click OK. A small window called ‘Load Legend’ appears. Click OK in this window as well.Then click ‘Apply’ in the legend editor window.
6.7. Zoom in on your map to remove pixilation problems, your BAKERMAP now looks like a USGS map!
7. Display the USGS map in shaded relief
7.1. We can shade our USGS map using the hillshade grid we created in step 3, above. This will make the map itself appear shaded and highlighted by the sun.
7.2. Witth the BAKERMAP theme as the active theme, open its legend editor, and choose the ‘advanced’ button at the bottom left.
7.3. A small window called ‘advanced options’ will open. Click on the drop-down box called ‘brightness theme’
7.4. Browse to the entry labelled ‘Hillshade of Bakerelev’ and click OK
7.5. Then, click Apply on the legend editor window.
7.6. WOW!