The FCC publishes a map of estimated groundwave conductivity of the United States, but the resolution is quite low:
Are there any GIS datasets that include groundwave conductivity at a higher resolution and with more precision? For example, at the arcminute resolution?
I've already converted the map into a shapefile, so I don't just need this map in GIS format.
I originally asked this question on the OpenData StackExchange, but it might be a better fit here because it's highly specific to radio.