Navigate to your DEMs folder that you created previously. Double-click on the DEMs folder to get into it, then type in a file name something like this: NOTE: The extension is very important. Do not fieldarea_DEM_projected.tif forget to add the .tif file extension. Click Save. Now you need to select the Output Coordinate System. This should be the same, projected coordinate system as the file dataset in your geodatabase. Scroll down in the window to see all of the other options. IMPORTANT: The default selection for the Resampling Technique is NEAREST. This is what you want. Click on the arrow to select BILINEAR. (See below for an example not comparison of what you will get with these two options.) No need to worry about anything else. Double-check everything. Click OK. This process takes a while, so be patient. Eventually, you will get a little popup window telling you that the process has completed. Go back to the preview window in ArcCatalog and look at the projected version of what you have downloaded. The overall shape should be quite a bit different (unless you are working at or near the equator). Now you can use this in the same map as the data in your file geodatabase. Why Bilinear rather than Nearest? See the grid pattern in the DEM on the left? That is the one projected with the NEAREST sampling technique. That is meant for discrete data rather than continuous data. The smoother DEM on the right was projected using the BILINEAR sampling technique. Creating a hillshade from a DEM Another typical operation is to create a hillshade one of those shaded relief background images – that you can drape other layers over to make the topography stand out. In ArcCatalog, reopen the Toolbox if you no longer have it open. Click on the plus sign next to Spatial Analyst Tools. Click on the plus sign next to Surface. Double-click on the Hillshade tool. For the Input Raster, select your projected DEM.
Navigate to your DEMs folder that you created previously. Double-click on the DEMs folder to get into it, then type in a file name something like this: fieldarea_DEM_projected.tif NOTE: The extension is very important. Do not forget to add the .tif file extension. Click Save. Now you need to select the Output Coordinate System. This should be the same, projected coordinate system as the file dataset in your geodatabase. Scroll down in the window to see all of the other options. IMPORTANT: The default selection for the Resampling Technique is NEAREST. This is not what you want. Click on the arrow to select BILINEAR. (See below for an example comparison of what you will get with these two options.) No need to worry about anything else. Double-check everything. Click OK. This process takes a while, so be patient. Eventually, you will get a little popup window telling you that the process has completed. Go back to the preview window in ArcCatalog and look at the projected version of what you have downloaded. The overall shape should be quite a bit different (unless you are working at or near the equator). Now you can use this in the same map as the data in your file geodatabase. Why Bilinear rather than Nearest? See the grid pattern in the DEM on the left? That is the one projected with the NEAREST sampling technique. That is meant for discrete data rather than continuous data. The smoother DEM on the right was projected using the BILINEAR sampling technique. Creating a hillshade from a DEM Another typical operation is to create a hillshade – one of those shaded relief background images that you can drape other layers over to make the topography stand out. In ArcCatalog, reopen the Toolbox if you no longer have it open. Click on the plus sign next to Spatial Analyst Tools. Click on the plus sign next to Surface. Double-click on the Hillshade tool. For the Input Raster, select your projected DEM.
2_DEMs_2014.docx