SPATIAL DIFFUSION

Primary questions of spatial diffusion theory:

> What is being carried?

> How are things carried across space? Who or what is the carrier?

> What kinds of things get in the way?

1. CARRIERS...

A. Expansion diffusion: Object/attibute (rumor) is transferred from individual to individual by direct contact / correspondence. The carrier retains the object even as the next person acquires it.

> Population of those possessing object/attribute increases over time. (logistic curve)

B. Relocation diffusion: Object/attribute is moved from one location to another by the carriers. Examples include "passing the buck" and migration of Mormans.

C. Contagious diffusion: Object/attribute is transferred by direct contact. Distance can be a major deterrent. Dread is often associated with this type of diffusion; you read about it in the paper long before it gets you.

D. Hierarchical diffusion: Object/attribute may leapfrog through geographic space in a systematic way.

> Usually moves through some hierarchy in which the attributes of the places in the hierarchy and the connectivity among the places are of central importance.

E. Waves of diffusion: Resevoir of object/attribute builds and then is diffused after some threshold level is reached. Natural outcome with biological processes (Rabies epidemics, etc.)

2. BARRIERS...

Analogs of physical waves and how they respond to barriers.

Absorbing: Diffusion stops cold.

Reflecting: Diffusion hits barrier and is deflected.

Permeable: Energy of diffusion wave is reduced but not eliminated.

3. SCALE