Jun 19, 2020
Free Geospatial Data Sources — An Attempt to Tame the Beast Part 1
This article will focus on where to access free basemaps for QGIS, satellite imagery, and DEM/DSM data sources.
In my last article, I advocated for open geodata since the open exchange of information fosters collaboration, innovation, and economic growth. We have an unused economic potential of several trillion dollars a year according to McKinsey, and while we constantly produce more data, a lot of it is opened to research and the public bit by bit. This is great and without a doubt our path to the future, but there is a different problem that so many of us working with geospatial data face all the time: Where can I find the fricking data I am looking for?
I honestly don’t know how many hours of my life were spent looking for geospatial data. A humble guess would be that we are dealing with triple-digit numbers here- probably enough hours to get in the best shape of my life. Especially leading the Earth Observation development at WeGaw, I need lots of different types of freely available data to develop and test the product: Satellite imagery, basemaps, shapefiles, weather models, and rasters about a wide range of topics for different geographies at different points in time. But there is no central database to find and access what is needed.
So today I want to start to share my list of the best free geospatial data sources I found while working at WeGaw and the years before, in the hopes that I can make some lives a little bit easier and contribute to open exchange and innovation. In the future I hope to add information on SAR tools, data portals, data sampling, search engines for geodata, and thematic maps.
This will be part 1 of probably 3. Partly because I doubt that putting everything in one post is possible without causing an information overload for you, the reader, but mostly because I severely underestimated how many resources I have bookmarked over the years.
Basemaps
Let’s start with honestly one of the biggest lifesavers I ever found when working with QGIS. This beauty of a script runs from the Python console inside QGIS. By copy-pasting it and simply hitting that “Run command” button, you’ll have 34 (!) different basemaps available inside your XYZ Tiles section. This includes several basemaps by Esri, Google, Stamen, Strava, Carto, and OSM.
This is a small selection of what awaits you in that treasure trove.
There is also this blog post from 2016, where you can directly download a variety of GDAL xml basemap layers that (unlike with some other types) allow you to adjust its transparency and other properties. Basemaps from Google Maps, Esri, MapQuest, Mapnik and others are available.
Satellite imagery
Of all the types of geospatial data, satellite imagery is probably the most accessible and well-organized category of all. Among the most useful data portals are the following:
- NASA Earthdata Search This portal provides access to an incredible selection of satellite data. After registration, you have access to both the original data at different processing levels as well as derived data like information on land cover, cryosphere, biosphere and atmosphere. Earthdata offers lots of different filters to narrow down your data hunt, such as filter by keywords, platforms, instruments, and data formats. Here you can access e.g. MODIS, VIIRS and Landsat data.
2. Sentinel Open Access Hub is where to go if you look for Sentinel imagery. Imagery of all the Sentinels is available here free of charge, giving you access to SAR imagery with Sentinel-1, optical data at great resolution with Sentinel- 2 and more specialized data products from the rest of the Sentinel family. The coverage is global, and if you need a platform to experiment with the data, ESA’s SNAP provides you with a framework to analyze, process, and visualize the imagery to your liking.
3. USGS Earth Explorer has one of the most extensive collections of satellite imagery. You can get information about any place on Earth up to 40+ years in the past thanks to the Landsat collection. Unlike some of its competitors, you can also access Digital Elevation Models (DEMs) such as ASTER and SRTM as well as hyperspectral imagery over the platform.
Talking about Landsat, this is a script for automated bulk downloads of Landsat-8 data products in Python. Enjoy!
The sources for free satellite imagery on this list are also the most well-known in the community, but this is because of the accessibility, and quality as well as quantity of data they provide. If you want to dig deeper, here’s a great post by GISGeography that introduces you to 15 of both the popular and the more unknown free satellite imagery data sources.
Digital Elevation Model (DEM) Data Sources
DEM and DSM data sets have become the foundation of so much work in the geospatial realm. Knowing the XYZ of a place is the key to make sense of your space and get the maximum out of your data. My personal favourites are:
- JAXA’s Global ALOS 3D World Provided by the Japan Aerospace Exploration Agency (JAXA), ALOS World 3D is a DSM available at approximately 30m (1 arcsecond) resolution and is known as the most precise global elevation data. You can download it per tile and in bulk.
2. ASTER Global Digital Elevation Model The current version (V003) of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) GDEM has improved horizontal and vertical accuracy compared to earlier versions. ASTER V003 also includes a global Water Body Dataset. ASTER is available at 30m resolution. Unfortunately, ASTER data is still has tiles covered by clouds in certain regions, such as Central Europe.
3. Space Shuttle Radar Topography Mission (SRTM) data is available on the USGS EarthExplorer. The data covers 80% of the Earth’s surface at 30 meters resolution. Since it is based on SAR and InSAR, cloud cover is not an issue. More information can be found here. Don’t want to register? Derek Watkins created a website where he offers direct downloading by tile without registration.
Fun fact: The USGS Astrogeology Science Center has the DEM for Mars. Data from the Mars Orbiter Laser Altimeter (MOLA) at a little less than 500m resolution has been used to make a Terrain Map of Mars.
If you want to know more, OpenDEM provides a broader overview over freely available Digital Elevation Models, their spatial extents, licenses and resolutions.
That’s it for now! If this list proves to be useful for other people, I’ll continue with additional resources over the course of the next weeks. Happy mapping!
Disclaimer: This list contains data sources I collected over my years working with GIS and EO data. While all of them offer data free of charge (some with, some without the need to register), please always check if the license is suitable for your activity, especially if you plan commercial use.
Also, this list — even once finished — is of course in no way complete. My hope is that it will grow with time. If you know an amazing data source drop a comment and I will try to update the list accordingly.
