  The geographical pattern of human dialects is a result of history. Here, we
formulate a simple spatial model of language change which shows that the final
result of this historical evolution may, to some extent, be predictable. The
model shows that the boundaries of language dialect regions are controlled by a
length minimizing effect analogous to surface tension, mediated by variations
in population density which can induce curvature, and by the shape of coastline
or similar borders. The predictability of dialect regions arises because these
effects will drive many complex, randomized early states toward one of a
smaller number of stable final configurations. The model is able to reproduce
observations and predictions of dialectologists. These include dialect
continua, isogloss bundling, fanning, the wave-like spread of dialect features
from cities, and the impact of human movement on the number of dialects that an
area can support. The model also provides an analytical form for S\'{e}guy's
Curve giving the relationship between geographical and linguistic distance, and
a generalisation of the curve to account for the presence of a population
centre. A simple modification allows us to analytically characterize the
variation of language use by age in an area undergoing linguistic change.
