Data Downloads: DEMs

There are four types of spatial data I download frequently for research purposes– aerial images, digital elevation models (DEMs), soil maps, and county or other political maps. You can learn more about the first type, aerial images, in one of my early blog posts about Google Satellite, OpenLayers for QGIS, and OGRIP. Today I’m going to share some data sources for the second type, DEMs.

For Ohio, OGRIP is an excellent source of geographically referenced data. To get to the data download portal from the main OGRIP page, navigate to the Services/Data tab on the main menu, then navigate to “GEOhio Spatial Information Portal” and click “Ohio Spatial Data Infrastructure – Downloads.” 

In the data download portal, you can use the search bar to find your area of interest (highlighted in the photo). You can also use the zoom bar on the left side of the map to move between county and tile scale data. Note that the data available is for the county highlighted in blue on the map. If you haven’t clicked a county or nothing is highlighted, the download menu at the bottom of the screen will be empty.

Usually when I need DEMs, I use the tiled DEMs for an entire county by downloading the second to last option on the menu for OSIP I.

After unzipping the downloaded file, you get a huge list of folders, each with a tile location. Opening a folder gives you a handful of files, and I highlighted the file I open as a raster in QGIS to view the DEM.

If you’re looking for DEMs for areas outside of Ohio, you’ll need to use other databases. I like the USGS National Map. The search feature works the same way as the OGRIP portal, and the data downloads are also similar.

DEMs are useful for all sorts of things. I use them for calculating terrain derivatives, which you can learn about here and here. Keep an eye out for future posts about other spatial data downloads!

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