I have check the outskirts entry in Cambridge's Dictionary and found out that I could use either on or in.
The factory is in/on the outskirts of New Delhi.
Since when have industrial estates become islands?!
But this sentence from this ELL book has puzzled me! Why would I use "on an industrial estate"? The natural choice is to use in.
Last year a new language school opened on an industrial estate on the outskirts of Saint-Jean-sur-Arc.
There are no examples nor comments about the "industrial estate" entry in Cambridge's dictionary; just the definition.
These two examples were quoted from COCA with "hidden in":
The elegant Dawoodi Bohra Shi'a Masjid in Northolt is hidden away in a London industrial estate.
And "work on":
This paper reports on an outbreak of abdominal pain and vomiting in 12 people who worked on a small industrial estate in rural Cheshire (in the United Kingdom).
Any comments?