###There're some rules that are overlapping a bit (at least in my mind).
1) with big areas we usually use 'in' (where? - in Greece, in Europe, in the Nothern hemisphere, in the field)
2) opposite to buildings (where? IN a building) grounds of combined nature (flat places + buildings on them) require 'at' preposition (at the airport, at a bus station)
It depends on the context, Romeo.
"at the airport" means at the physical location, but "in the airport terminal"; "at the bus station [physical location] versus "in the bus station" [the building]
3) and I can't figure out or find anywhere a rule for using 'on' with areas.
It looks like this preposition is usually used with different places near water which somewhat rise over the water level (on the bank, on the Avon, on the coast, on an island - if the island is not very big. If the island is big, then we should use 'in' like with other vast areas.
Use 'in' if it the name of an island. To say that "he's in the island" would mean underground, inside the island.
Having at last lost myself here I would like to know which preposition we should use with the words 'ground', 'stadium', 'football field', 'beach', 'site'.
AT the sports ground or ON the sports ground (or playground)? (I've seen 'IN' as well)
With 'stadium' all the three prepositions are used regularly - according to what I see.
The player is scoring a goal on the field or in the field?
Gotta run and check on the cattle. Following the ideas I've given you, why not try to make some examples, with enough context, to see how you do?
Thank you very much for your educational help.
Also I wonder which 'where' prepositions go well with the words 'picture' and 'page'. The problem is that I can find examples of very different usage.