Does any open global georeferenced dataset on ground slope exist? Precision of 0.5x0.05 degrees longitude-latitude would suffice.
With-out a clear definition of ground slope (no Wikipedia definition), I am assuming it basically is proportional to the gradient of a topography data set. These are available at a resolution of 0.002 deg.
Ignoring earth curvature at that resolution, a simple two dimensional numerical differentiation should suffice.
Please correct me, if I am wrong.
I have no idea whether this is acutally the same dataset as linked to by user Grimaldi in his answer, but OpenStreetMap seems to rely on the SRTM dataset by JPL to calculate its height maps and contour lines. From the release notes of the latest SRTM update (from 2014):
Previously, SRTM data for regions outside the United States were sampled for public release at 3 arc-seconds, which is 1/1200th of a degree of latitude and longitude, or about 90 meters (295 feet). The new data have been released with a 1 arc-second, or about 30 meters (98 feet), sampling that reveals the full resolution of the original measurements.
Concerning the slope question: refer to Using SRTM Global DEM for Slope calculation on the GIS.SX for extensive answers (some targeting ArcGIS, some not) and discussion of subtle issues when dealing with global coverage data. Just as an appetizer: there is