If you get sent 500 bitcoins, they can all be traced back to generation transactions, so you "own" a bunch of little pieces of land in bitcoin-world.
You can number generations that way, but once any multi-output transactions take place, any numbering is lost. "Which output got bitcoin #5"?That's easy-- if #5 is the lowest ordinal piece of dust, then it goes to the first txout. Etc.
It's all arbitrary but deterministic, and all recorded in the block chain, so you could define rules to trace every .0000000001-of-a-bitcoin forward through transactions.