Grammar Girl here, today we'll be looking at two constructions that are correct, but

which one you choose depends on your audience.

The expressions that concern us today are which and where.

We'll be comparing sentences like these.

This is the store at which I met my friend, and this is the store where I met my friend.

As you can probably guess, which is more formal than where.

In the two sentences about the store, the words which and where, both function as relative

pronouns.

Relative pronouns, such as who and that, introduce dependent clauses.

So in the sentence, the dog that I adopted needs its shots.

The clause that I adopted is a dependent clause headed up by the relative pronoun that.

The relative pronouns which and where specifically describe place.

If you wanted to discuss where you adopted the puppy, you might say, the pound at which

I found spot was on state street.

That's a pretty formal sounding sentence though.

You might say that sentence in a courtroom or in another formal situation.

Other than maintaining formality, there are two valid reasons you might want to use which

instead of where.

Many times you can add a preposition before the relative pronoun which to make your sentence

quite precise.

For example, the house at which I saw you has a slightly different meaning from the house

in which I saw you.

...