Prepositions of place

At and on

We use at to show a specific place or position.

For example:

 Someone is at the door.

 They are waiting at the bus stop.

 I used to live at 51 Portland Street.

 

We use on to show position on a horizontal or vertical surface.

For example:

 The cat sat on the mat.

 The satellite dish is on the roof.

 

We also use on to show position on streets, roads, etc.

For example:

 I used to live on Portland Street.