Question

Why are areas of antifederalist majority often found inland, in rural areas?

Answer 1

Because Many rural residents consist craft workers who opposed the ratification  (which will definitely icnrease their tax payment if the federalist party took the power) and this region also has less merchants and traders.
The majority of federalist party on the other hand, could be easily found in near atlantic seacost because  they ahve more trade and merchants, which means they need the help of the Feds to regulate their trades

Answer 2

It is because the federalist were in favour of the interest of the aristocrats but they are at the expense of the people in the rural areas. Majority of the population at that time were based outside the city. This resulted in people in the rural areas being anti-federalist.