system
Given the following post, respond as if you're commenting on Reddit:
human
[Fullmetal Alchemist] What is the farthest distance an Alchemist can transmute?

Like could Ed transmute on one side of central city to affect the other side?
gpt
Normal alchemy has its effect centred within its transmutation circle, though the line of effect can extend beyond it. Example of distance alchemy like that include Armstrong's artillery rocks (where the transmutation is instant but the rock is thrown by force) and Mustang's flame alchemy (which is considered extremely complex, in that the effect really is centred on his hands BUT travels through the air with precision to the target at virtually lightning speed).

People like Ed are somewhat of an exception due to their not using a circle, but the general limitation remains where the transmutation is centred on their point of contact (where his hands touch usually, though sometimes he channels out of himself elsewhere like his feet). He can achieve a limited degree of distance alchemy, but only where the effect is extremely basic because he's actually changing everything from where he's standing TO where the effect is occurring. That's why his little "create stone walls" trick is actually so mindblowing: nobody else can do anything nearly that complex, AND he does it on the fly meaning they can come out of anywhere.

To affect something across Central, there's a few ways this could be accomplished. Option one is explored in the series: just make a giant transmutation circle that encompasses both you AND is centred on the location you're trying to affect. But that's not what you're trying to do.

Option two, which is Ed's style of alchemy, would require him to have clear line of sight AND line of effect across that distance. With your example of Central City, that's definitely impossible due to buildings. So let's move this out into an empty field. Now, he needs to know what he's doing... as well as the composition of *everything between him and his target*. This isn't technically impossible, but it sure takes out 99% of opportunities. So again, let's move. Maybe a perfect stone plateau? It's now a safe bet that the ground is "stone" (whichever stone that may be) from here to the target location. *Now* he could make a statue appear from across that massive distance, by knowing all the necessary details.

Option three is abandoning alchemy, and switching to alkahestry from Xing. It's specifically focused on distance transmutation, as long as it's along "ley lines" which alkahestry practitioners can somehow identify. Drop a circle on the opposite side of the city, trace a linkage to where you are and make a mirrored circle, and voila!