It's a simple empirical question. Well, strike simple... Whether something is part of the same supply--or demand--depends essentially on how fungible the goods

It's a simple empirical question. Well, strike simple... Whether something is part of the same supply--or demand--depends essentially on how fungible the goods/labors in question are. Let's say you have two similarly skilled groups of rockstar ninja programmers on two isolated planets. No matter the groups' similarity, it'd be silly to consider them part of the same supply. The way to establish this empirically would be to clone a group of identical programmers on Kepler 62e and see if that influences labor prices on Sol 3. If it doesn't, they're not part of the same supply. Which is what economics predicts you'd see, since there's no way for employers on one planet and programmers on the other to interact. Now consider the Bay Area market. If you doubled the number of programmers here while maintaining a consistent composition of skills, you'd probably see compensation drop. Which brings us to, do programmers form a global supply source and do employers for them form a global demand source? And the answer is... jein, though on the whole there does seem to be distinct national and regional markets, coupled together with various levels of porosity. Of course, the obvious complaint is that our policy choices--restrictionist immigration regimes--have created the markets we work in. And that's a fair complaint! And that's always the most vexing thing about economics. There's no natural order of things that we can lean on to push naturalistic fallacies. Things are what they are. If they changed, things would be different.