John Elledge has a great post showing something I talk about often as data journalist - the most interesting thing about a number is how we conceptualise or define it, rather than the number itself.
In this case, is the Amazon river longer than the Nile?
The issue at the root of this particular row involves the knotty question of where a river starts. The source of the Nile has traditionally been given as Lake Victoria...
...The problem is that it’s very obviously no such thing. The water in lake Victoria doesn’t just appear there out of nowhere, but generally comes from other rivers which flow into it...
Knowing which tributary to measure is far from the only difficulty. There are problems at the other end too: when, exactly, does a river stop being a river and become instead the sea? “Where it starts being tidal” seems momentarily a good, objective answer – until you realise it means the big watery thing flowing through London should no longer count as the Thames.
