GTOPO30 is a digital elevation model for the world, developed by United States Geological Survey (USGS). It has a 30-arc second resolution (approximately 1 km),  and is split into 33 tiles stored in the USGS DEM file format.
- USGS EROS Archive - Digital Elevation - Global 30 Arc-Second Elevation (GTOPO30)
- "Accuracy". Retrieved July 26, 2017.