Diffusion is the spread of ideas to other areas. For example, the Southern Baptist Church began in the South, now it is found in many other countries. In the same manner, cattle were once found only in the Middle East. Today they are found over large parts of the world. Coffee was once grown and consumed only in Ethiopia, today much of the world drinks it.
Mental maps are fascinating.
Take a look at the ones on page 15. My guess would be a mirror opposite of the two maps depicted. We may define culture as a learned set of behaviors. It is not genetically passed down. Often the maps show diffusion.