Each concept here is mapped to its prerequisites — the ideas you'd need first to understand it — all the way down to four foundations: Space, Time, Energy, Pattern. Click any prerequisite to drill down, or scroll for the chain graph.
A vast desert of mobile sand dunes, particularly extensive sand seas found in major deserts like the Sahara, characterized by a quantity of sand dunes.
External reference — all senses of the word “erg” on Wiktionary. This atlas concept maps to only the slice of meaning relevant to the prerequisite graph.