At or In

There is no strict rule, but we tend to use 'at' for specific places and small villages etc and 'in' for larger towns, cities, counties, states countries, continents etc.

Cen prolly right as usu, but good q Paok, never ast myself. You're to be congratulated for your determination to learn a difficult language. When I inquired of my Better Half, who is much smarter than me, she responded that 'in' is more colloquial

I had thought 'in' implies more direct participation. For instance he might have showed up late, couldn't sign in, but they let him run anyhow; so, 'at'

But mine's a real stretch

Maybe more colloquial to use 'in' rather than 'at' with small places, villages or hamlets, but to say somebody lives or is 'in' London (or any city or town) is absolutely standard and not a bit colloquial. To say they live 'at' London (or Glasgow or Chicago) is just plain wrong.

Wow Cen, it's just too subtle for me. 'Way beyond me after some 80 year in the very field. But don't you find it remarkable where so many esl like 1970 here get so totally engaged