AT versus IN when referring to location

[Rita]

It has come to my attention recently, while reading newspapers, mags and books, that writers are choosing "at" when describing the condition of being at a place, i.e. "I am AT St. Simons Island vs. I am IN St. Simons. I personally prefer (actually feel more comfortable) with the preposition IN. Which is correct? Also, I say, I am AT the lake 'cause, of course, in that case, It would be silly to say I am IN the lake unless I actually was. What about I am in the mountains vs. I am at the mountains or I am at Stratford on Avon vs I'm in Stratford on Avon. And, I am at the drugstore vs. I am in the drugstore. Any hard and fast rules on this?

Many thanks

Rita

[Tom]

Hi Rita

Sometimes they are interchangeable and many a time they are not!

If a place is big then we should use in.See below:

He was in America at a party in San Francisco.

She was in London at Oxford Universiy.

Tom

[Yankee]

Hi Rita