By analogy with the physico-chemical theory of dissipative structures, or with synergetics: in a dynamic system, qualitative change of structure which may be generated by an amplification of a small internal fluctuation or by an external perturbation, when the system is in an unstable state. Bifurcations are theoretically unpredictable, they drive the system toward a […]
Obstacle to the extension of a diffusion process, which thus often acts as a limit between two geographical subsets. A barrier may be physical (mountain, ocean, river), linguistic (border), social or cultural (inequality in access to information, religious resistances, taboos etc…)
Mathematical theory developed by R. Thom in order to formalise the behaviour of systems where the continuous change of value of a parameter is susceptible to locally introduce discontinuities in the evolution of state variables. These ruptures have been rigorously described and classified by means of a number of state variables lower or equal to […]
Concept analogous to that of market in economy; supply and demand for services meet and exchange in places privileged for their accessibility, which are central places. 1. In a network, it characterises the position of nodes in terms of accessibility (see centrality index), the centre being the place endowed with maximal accessibility; 2. For a […]
Model elaborated by the German geographer Walter Christaller in 1933, derived from the central places theory which gives account of the size, spacing and number of cities. The model describes the hierarchical organisation of a network of cities according to the level of services they provide, and their regular spatial disposition on the vertices of […]
Term of psychology, relative to knowledge processes (acquisition, storage, use and processing of information), used in geography of perception, or of representations, or of experienced space; relative to an individual or collective representation of space, in function of a knowledge or of a practice. The cognitive map (or mental map) designates either this mental representation, […]
In theory of graphs, intensity of interlinking between nodes through edges of a network; more generally, degree of internal connection of a network. As opposed to mere proximity relations, called relations in continuity, connectivity relations are those using the support of a network to link two places that may be far apart from each other.
(from Latin contingere “to touch”) Two geographical units are contiguous if they have a common border. A contiguity matrix is a square table whose cells indicate (generally by means of one or zero) whether the geographical units mentioned in row and in column are contiguous or not. A contiguity constraint may be added to a […]
Interval to cover in order to go from one place to another, distance has a meaning of separation, its covering requires effort, expense of energy. The mathematical definition of distance is restrictive: a measure of gap between objects is a distance if it is symmetrical, if it is not negative, if it is null only […]
(from Greek dynamis “force”) Process of change, or evolution, resulting from action of forces: the dynamics of unequal exchange produces a centre-periphery structure. Dynamic models link changes with the forces that generate them, whereas kinetic models describe changes without reference to forces. In human geography, the term dynamics implies a notion of change, and not […]