My understanding was there's basically three zones - North and South America, Europe and Africa, and finally Asia and SW Pacific. So as OG has already said, it doesn't matter which order the continents are done, apart from making sure you match the zones (so you couldn't fly SYD-JHB-HKG, but SYD-HKG-JHB or HKG-SYD-JHB are both fine).

Within the zones and continent restrictions, anything goes. So for instance, you could fly MAD-SCL-IPC-SCL-NYC if you wanted to wander to the extremes of the zones and still stay legal (and I'm sure you could stretch things much further than this too ). No doubt others can clarify on my late night ramblings, but hopefully you get the basic gist of things