The preposition at is used in the following descriptions of place/position:

With specific places/points in space

• She kept the horse at a nearby farm.
• I had a cup of coffee at Helen’s (house/flat).
• Angie’s still at home.
• I’ll meet you at reception.
• There’s a man at the door.
• I saw her standing at the bus stop.
• Turn right at the traffic lights.
• The index is at the back of the book.
• Write your name at the top of each page.

With public places and shops

• Jane’s at the dentist/hairdresser.
• I studied German at college/school/university.
• Shall I meet you at the station?
• We bought some bread at the supermarket.

With addresses

• They live at 70, Duncombe Place.

With events

• I met her at last year’s conference. She wasn’t at Simon’s party.

The preposition on is used in the following descriptions of place/position:

With surfaces, or things that can be thought of as surfaces

• The letter is on my desk.
• There was a beautiful painting on the wall.
• The toy department is on the first floor.
• Write the number down on a piece of paper.
• You’ve got a dirty mark on your jumper.
• He had a large spot on his nose.
• She placed her hand on my shoulder.

With roads/streets, or other things that can be thought of as a line, e.g. rivers

• The bank is on the corner of King’s Street.
• Koblenz is on the Rhine.
• Bournemouth is on the south coast.
• It’s the second turning on the left.

The preposition in is used in the following descriptions of place/position:

With geographical regions

• Driving in France is very straightforward.
• Orgiva is a very small village in the mountains.

With cities, towns and larger areas

• Do you like living in Nottingham?
• They were having a picnic in the park.
• She works somewhere in the toy department.

With buildings/rooms and places that can be thought of as surrounding a person or object on all sides

• Can you take a seat in the waiting room, please?
• I’ve left my bag in the office.
• There’s a wedding in the church this afternoon.
• Lots of people were swimming in the lake

With containers

• There’s fresh milk in the fridge.
• I think I’ve got a tissue in my pocket.
• The money is in the top drawer of my desk.

With liquids and other substances, to show what they contain

• Do you take milk in your coffee?
• I can taste garlic in this sauce.
• There’s a lot of fat in cheese and butter.

A general pattern again emerges if we consider these different aspects of usage. We can think of at as one-dimensional, referring to a specific place or position in space. On is two-dimensional, referring to the position of something in relation to a surface. In is by contrast three-dimensional, referring to the position of something in relation to the things that surround it. Thinking of the prepositions in these terms helps us explain certain facts. For instance, in is generally used for larger places and at for smaller, more specific places, so we say:

But:

However, if we think of a city or larger place as a specific point in space, we can use at, e.g.

Or if we think of a smaller place as three-dimensional, we can use in, e.g.