Prepositions 2: On or In?

Prepositions of place using 'on' and 'in'.

He lives.....

on the mountain but in the mountains
on the border but in the border region
on the island of Tobago but in Iceland
on the ocean (if he lives near it) but in the ocean (if he is a fish)
on the edge of the city but in the city
on Fifth Avenue but in Brooklyn

He lives....

in the desert, in the forest, in the countryside, in the suburbs, in the outback, in the park, in heaven (or hell), in a prison, in a hospital, in a hostel

but

on a farm, on the coast, on the moon, on Mars, on a slope, on the horizon, on the outskirts, on a reservation, on a campsite, on a housing estate, on the web

Note: On the route to China is usually written en route to China

Can you see a pattern here? In general, in is used with places that have specific boundaries or walls. On is used with surfaces or sites where there are multiple dwellings. But it's a fine line sometimes between on and in.

A word like territory can take either in or on:

The crime took place in the territory of the former Yugoslavia. (= specific territory)

The incident took place on enemy territory. (= more abstract or relative)

Compare these examples:

It happened in your garden.

It happened on your territory.

Can you see the difference?