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

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.

...........................