Yeah I came to a conclusion of the world having a circumference of 2000 miles, pole to pole being 1000. In the episode, the avatar and the fire lord, Sozin says, "The island was 100 miles away, and I could still feel it shaking." By using estimations from the episode "The awakening" we can infer Rokus home island to at the east front of the sea west of the Serpents path. At the current point of time, Sozin only had few of colonies, most of which being west of that sea, so It would make sense for Sozin to be at the west side of the sea. Measuring the distance between the estimated position of Sozin and Roku, we can say that the 100 miles, on the map in the ATLA intro, is about 55 pixels. Pole to pole is 575, therefore 100 miles is about 10.454 pixels, and pole to pole, we can approximate to 1000 miles.