"ar an" vs "sa" for placenames?
what is the difference between ar an and sa (in in english ) e.g. ar an gCeathrú Rua vs sa Cheathrú Rua (in Carraroe ) and ar an Tulaigh vs sa Tulaigh (in Tully)
With localities that have an article, ar an (and ar na) are generally better than sa (and san and sna) for translation as “in”, e.g.
Ar an mbaile seo, in this town. Ar an gCnoc, ar na Cealla Beaga, at Knock, in Killybegs.
Note that “at” can sometimes be preferred over “in“.
Sa (and san and sna) are generally used more for “generic” places, e.g.
Ag obair sa chathair, working in the city. Amuigh sa gharraí, out in the garden. Thuas sa spéir, up in the sky.
Sa and friends would also be used for larger named places — regions, countries, continents, etc.