I heard this expression quite a bit when I was in Japan, and because of context took it to mean pretty much what it sounds like in english. Ah, so you want a ticket to Tokyo, eh? I also, initially at least, took “hi” to mean “hello”. Those poor, patient waitresses had heard it all a million times and still acted like they thought it was funny.
Anyway, what does the ticket agent mean when he looks at where I point on the schedule and says “Ah so”.
Peace,
mangeorge
remember the old saw that the Japanese have trouble pronouncing the letter “L?”
He was calling you an “asshole!” 
Basically, it just means “ah, ok” or “got it.” If it’s pronounced like a question, it would mean “really?”
Also, the ‘o’ is usually stretched out for an extra beat, so it’s usually romanized as ‘soo’.
You might also hear the slightly more formal “soo, desu” which means “that’s right,” or “soo, desu nee” which means “yeah, that’s true, isn’t it?” and is usually accompanied by a lot of nodding and agreeing.
“soo ka na,” however, means roughly “I don’t think that’s correct.”
Anyway, what does the ticket agent mean when he looks at where I point on the schedule and says “Ah so”.
Depending on context it can mean a couple of things but in this circumstance I would interpret it as “I see what you mean”. It can also mean “that’s right”.
While I don’t know for sure, the other posters’ answers do seem to make sense. Think of it as “shorthand” for “ah, so it is.”
The “ah” part = “oh” in English.
The “so” (or “sou,” if you wanna get picky about romanization) is somewhat equivalent to “that.” The man left off the copula “desu,” which is common in spoken language.
anyway, “ah, sou desu” would mean “oh, that’s it,” or more naturally, “oh, I see” in English.
My nickname is the informal way to say “soo desu, ne”. Desu becomes da, and I shortened the o so people don’t call me Sue.
They even had a boy named ‘Sue’ in Japan?
And you typically won’t here the “u” in “desu” pronounced, especially by men.
You’ll hear: “Ah, soo des” with the “oo” denoting long o, not the typical English “oo” of “look” or “book”.
Bit of fun trivia: in my neck of the woods it’s “so ya ne.”
[hijack]
I studied a bit of Japanese in college, and I seem to remember hearing that Kansai-ben is far enough removed from standard Japanese that people who speak the two dialects sometimes have difficulty understanding one another. Is that actually the case? It just seems odd to me that two dialects in such close physical proximity would be so different.
[/hijack]
Anyway, what does the ticket agent mean when he looks at where I point on the schedule and says “Ah so”.
Sometime “ah so” implies that sometime need to be considered. If it were a slam dunk request, he may just say wakarimashita. ah so and ah so desu ka are also often used after hearing bad news, such as when one’s request is denied, but that wouldn’t be the case here.
I take it that the word “so” being used to answer a question (meaning “yes”) is the same word as in “sô desu”?
First of all, it depends on what generation you are speaking to. Some of the older folks (say, in their 70’s and above) are nearly impossible to understand. Their speech is fairly removed from standard Japanese. Also, they speak in sub-dialects of Kansai-ben, so a person from one village may speak quite differently than a person from a village not 50 miles away.
However, the language I hear spoken by younger people is much easier to understand. I believe that Kansai-ben, and most other dialects, have been watered down over the years, so it’s not difficult to figure out what they are saying from context. The vocabulary they use is not so different - perhaps it’s comparable to American vs British English. Anyway, I had little trouble figuring out what people are saying. As for native Japanese, there are many entertainers from the Kansai area on TV and in the movies, so people are fairly used to hearing Kansai-ben.
On the other hand, the dialects of more remote prefectures, such as Akita and Kagoshima, are really, really different. I heard some Akita-ben once, and it may as well have been Korean.
Sorry about the hijack.
Yes. It’s like saying, “that’s so” or “that’s right.”
It wouldn’t be ‘so ya na’?
It could be either “na” or “ne,” but you’re right - “na” is more common than “ne,” whether spoken by men or women. My bad.
Actually, it depends on where you are. “Ya” for “da” is associated with Kansai but it’s used commonly in other areas as well. You get every permutation of “sou/se”, “da/ya”, and “na/ne”. Around here, “so ya ne” is standard.
Additional info about “so”:
One of the fundamental elements of Japanese grammar is known as the ko-so-a-do. “Ko” refers to that which is close to the speaker. “So” is close to the person being spoken to, “a” is far from both and “do” is a question. Those aren’t words in themselves but many words are formed from these syllables. For instance:
Kore: this thing (close to me)
Sore: that thing (close to you)
Are: that thing over there
Dore: which one?
“So” is part of the following series:
Kou: this way (as I’m showing/telling you)
Sou: that way (as you’re telling me)
Aa: that way (as something over there is showing)
Dou: how?
True, but we’re both talking about Kansai 
Just out of curiosity, what would you say the “ya” vs. “da” ratio in Gifu is?
Oh, sorry about the double post, I forgot about this:
I used to live in a very rural, very remote fishing village. Even though the town didn’t have such a large population, it was spread out over a number of little hamlets that were often separated by hills or even small mountains. I lived on the eastern side of town and the people there used to make fun of the way people on the western side of town spoke. Some people were very proud of their local sayings or vocabulary. “Local” here meaning a 200-people hamlet.
Actually, there is a big difference. American and British English mostly differ by accent and relatively accidental vocabulary, e.g. lift/elevator, flat/appartment, etc. There is the same thing happening with Kansai and Kanto Japanese (naosu/katazukeru, akan/dame) but the biggest differences are at a very basic level, unlike English. The almighty copula is different, negatives are formed differently, final particles are different, and polite keigo language works differently in some areas.