on = surface/medium — the core rule (GiU Unit 123-124)

The core

on = a surface / attachment / medium you lay things against or ride.

on (surface/medium)	why
on the map · on the page · on the list	flat surface carrying content
on the computer · on my phone · on the internet · on the screen	device/medium
on the wall · on the ceiling · on the table	attached to a surface
on the corner (street) · on the pavement · on Broadway	a point on the street plane
on a tree (leaves) · on the wall (picture)	growing/stuck against
on page 53 · on the bus · on TV	medium / ride-on
on the left / on my right · on the coast · on the border	line or side

The three-way split

preposition	idea	examples
on	surface, attachment, medium	on the wall, on the map, on the internet, on the corner
in	enclosed or inside a substance	in the box, in the water, in the corner (room), in the photo, in the newspaper
at	a point / venue / location	at the door, at the station, at the corner (point), at home, at the hairdresser’s

Same noun, different preposition

in	on
in the corner (of a room)	on the corner (of the street)
in the photo (inside the frame)	on the photo? ✗
in a car / taxi (enclosed)	on a bus / train / plane (ride-on)
in the wall (embedded in it)	on the wall (hung against it)

Test

Ask: against/on a surface or medium? → on. Inside something? → in. A point or a venue where something happens? → at.

Source

Raymond Murphy, English Grammar in Use, Units 123–124 — in, at, on (position). Ebot lesson 2026-09-05.