Dragon Lord Thorn addresses the dragons he summoned as "Dragons of Equestria". Yet, several scenes in the exact same episode seem to disprove this, (see image).
I am well aware of the official map of Equestria as seen here:http://www.equestriadaily.com/2015/10/official-map-of-equestria-updated.html
^Judging by that the "Dragon Lands" should be located in the bottom left-hand corner.
I went back and watched Dragon Quest in order to potentially sort out the contradicting statements I found in Gauntlet of Fire, but that proved even more confusing (see left hand side of image).
Dragons migrate TO the Dragon Lands very rarely. Dragons are summoned by the Dragon Lord TO the Dragon Lands on occasion. Where are they migrating FROM? This is the question I seek an answer to.
If we take into consideration what transpired in the S1 episode Dragonshy, we can deduct that it is not normal for full-grown dragons to take up residence in Equestria as a whole. In Owl's Well That Ends Well, Spike stumbles upon a full grown dragon's cave. Judging by the facts that Spike was walking on foot, and not for very long, we can clearly assume it was relatively nearby Ponyville.
^This seems to imply that Dragons are generally not welcome in Equestria, yet some manage to ignore these unspoken to varying degrees of success. Now once again, the question is where are these dragons supposed to reside, if Equestria is off limits? Judging by their flight patterns during migration, and how they tend to stay in a straight line until they reach their destination, it's likely they come from somewhere around the Northwest of Equestria. They pass right over Ponyville, so you can use that to determine their trajectory.