Full Idea
A sand dune depends on the individual grains of sand that make it up. In an important sense, however, a line's segments depend on the line rather than it on them.
Gist of Idea
Dunes depend on sand grains, but line segments depend on the whole line
Source
John Heil (The Universe as We Find It [2012], 03.4)
Book Reference
Heil,John: 'The Universe as We Find It' [OUP 2012], p.40
A Reaction
The illustrations are not clear cut. As you cut off segments of the line, you reduce its length. Heil is hoping for something neat here, but I don't think he has quite got. The difficulty of trying to do pure metaphysics!