  Cultural competition has throughout our history shaped and reshaped the
geography of boundaries between humans. Language and culture are intimately
connected and linguists often use distinctive keywords to quantify the dynamics
of information spreading in societies harbouring strong culture centres. One
prominent example, which is addressed here, is Kyoto's historical impact on
Japanese culture. We construct a first minimal model, based on shared
properties of linguistic maps, to address the interplay between information
flow and geography. In particular, we show that spreading of information over
Japan in the pre-modern time can be described as a Eden growth process, with
noise levels corresponding to coherent spatial patches of sizes given by a
single days walk, and with patch-to-patch communication time comparable to the
time between human generations.
