From tests, the order appears to be:
- controlling station first
- all other assets in order of either population or economy size (I haven't been able to find a test case where the ordering of population and economy size differs, and in almost all stations there'll be a 1:1 relationship between the two anyway)
I've not seen any exception to that rule in any case where the population/economy size parameters were measurable accurately.
In normal fully-procedural systems that's generally going to mean large stations, then outposts, then Odyssey bases, then the non-dockables as they don't add population - but not always. In systems where Frontier has been hand-placing assets, the order is more likely to be atypical.
Economy size you can usually get a proxy for by checking the H-Fuel stock (either in None state, or adjusting for the state effects), though note that Colony economies sell way less H-Fuel than you'd expect based on that, and Odyssey settlements can be all over the place, so it's not a perfect indicator. Obviously where the dockable doesn't have a market and you don't have a before/after on its addition to compare population, you're on your own a bit.