Most of this is googleable but there are thousands of traders that make sure the gold price is the same globally so nobody had to “move” their gold in the reverse for this trade to work.

The difference between London and the US is that the bars are of different size (12.5 vs 1kg).

The price of gold is not equal globally, there is a ‘loco swap’ price differential, reflecting the price of moving the metal, eg flights, security, tariffs that may be attracted, whether the location can service futures delivery etc

> there are thousands of traders that make sure the gold price is the same globally so nobody had to “move” their gold

Physical versus contract differences are real and require moving the actual gold. What most users do is sell deliverable where they want it out and then buy contracts or deliverable where they want it and then let the market figure out how to move gold around to settle. (It probably won’t involve moving gold from where you had it to where you want it unless you’re in a cohort.)