5.1. Introduction

Diffusion processes occupy a place of choice in the expression of dynamics affecting spatial systems. Certain characteristics of these processes justify the importance given to them in the spatial change component inventory as well as in a presentation of the methodologies explaining their features. We will also add that the studies on spatial diffusion of innovations can be considered as precursor studies paving the way for the contemporary attempts to model spatial change.

A brief terminology reminder will be useful in introducing the chapter. Generally, by diffusion we mean the action, and the result of the action, of propagating an object in a homogenous way or transmitting the object or a phenomenon in a system whatever the propelling power. At the end of the process, the system is saturated. Its absorption capabilities are exhausted. The system invested by this action tends to go from one state to another. The notion of diffusion is therefore mobilized every time we study processes that involve movements of matter, products, people, intangible goods, practices or ideas for penetrating a system. Due to this, the diffusion processes are addressed by physical as well as biological and human sciences.

Social sciences in general and geography in particular often associate diffusion and innovation (see Box 5.1). In its most trivial sense, innovation simply represents the newest thing (material or intangible) that, when it appears for the first time, is adopted by a person or a group. We have also studied...