Depicting floods using higher resolution elevation data
Using Depiction to create and display floods requires having elevation data. The elevation data available through Depiction’s Quickstart resource list is from the United States Geological Survey (USGS) – it is their default “30 meter resolution” – in other words, every 100 feet or so, it measures the height of the terrain. In general, this is good enough for big picture stuff.
For community or neighborhood level flood depictions, higher resolution elevation data works much better. You can access 10 meter elevation data from the USGS NED (National Elevation Dataset) site at http://seamless.usgs.gov/index.php though the process is bit cumbersome. Fortunately, there are other sites where publicly accessible 10 meter DEM (Digital Elevation Model) data can be found, easily downloaded to your computer and imported into your depiction.
For Washington State, this data is available at http://duff.geology.washington.edu/data/raster/tenmeter/byquad/index.htm…. Here’s how to include this higher resolution elevation data in your depictions if you’re in Washington State:
- Make sure you’ve already added (using Quickstart) the default 30m elevation data
- Click on the quadrant on the map at the above webpage that contains the area you’re interested
- You’re taken to a new map where you click on the city or community where you’re doing your depiction
- When the file download window appears, choose Save and save the zipped file to your desktop
- On your desktop, unzip/extract the zipped file and you will get a file of about 8mb with a name like “q722.dem”
- In Depiction, go to Add Content, choose “import from” File and browse to the .dem file.
- Under Select definition, choose Elevation and click Add
- Depiction will now load the .dem elevation file, and replace the 30m data with the more precise 10m data wherever they overlap
Below are screenshots that show the difference in a flood depiction when going from the 30m to 10m elevation data. Higher resolution elevation data should be available for where you live – just search for a public resource on the web. In addition to elevation files with a .dem extension, Depiction will also import elevation data files with the following extensions: .hgt, .gtiff, and .adf.