Real and apparent time clues to the speed of dialect diffusion

In contrast with the traditional dialect atlas, the glottogram simultaneously displays geographical differences and age differences in language usage.1 There are two techniques for ascertaining the absolute chronology of linguistic change: real time and apparent time techniques. The typical technique for the apparent time is the comparison of two dialect maps of different age groups. There is another technique for considering geographical and age differences at the same time. This technique, called the “glottogram”, has the merit of offering clues for the speed of diffusion. In this paper, several examples of dialect maps and glottograms showing speed of diffusion will be observed. The speed of diffusion within one community may be somewhat more than three generations or around 100 years. In the same period of one century, the changes typically proceed 100 km from the community.