A preposition + a noun phrase (NP) or a noun equivalent.

a) The students at the back come from York.

b) The boys on the corner are playing pokemon cards.

c) The girl in Jeans is my twin sister.

d) I met a man in a gray suit.


The preposition that performs as an adjective equivalent gives more information about a noun.

In the first example, the students "at the back" comes from New York. "At the back" gives a description about where the students are not the means whereby the students come from New york.