Gradient

Articles

• Spatial structure
  6 August 2004, by B. E., Th. St.-J.

  The word "structure" comes from Latin struere which means to build, to arrange, and contains the notion of an organised thing. Spatial structures exist, because geographical space is not constituted by a set of unique places, occupying random locations. The successive choices of actors and, more broadly, the answers given by societies to the issue of space control , obey to certain logics, even if the overlapping and interweaving of these logics make their legibility more or less evident; (...)

• Distance
  6 October 2004, by D. P.

  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 when two objects merge, and if it verifies triangular inequality. A space endowed with distance in the mathematical meaning is a metric space. Observed or cognitive geographical (...)

• Neighbourhood
  26 August 2004, by D. P.

  The term neighbourhood is used for everything that is close, nearby, contiguous. Distance as measure of separation, of interval between two places may not be dissociated from the definition of a neighbourhood. The neighbourhood reaches its limit point (immediate neighbourhood) when the spatial units are contiguous, adjoining. A neighbourhood is always expressed into a metric space. The measure of topological relations may be used to express contiguities between objects or places which are (...)

• Gradient
  6 October 2004, by D. P.

  Is called gradient the variation of intensity of a phenomenon per unit of distance between a place and a given centre (or axis). It is the case for example with density gradients which develop around a city centre, gradients of population, facilities, shops, services, gradients of land prices, etc. gradients of population which appear on either side of some traffic ways or else starting from a coast, etc. Geographical gradients are the expression of the fact that places belong to fields of (...)

• Polarisation
  12 January 2005, by B. E.

  The concept of polarisation covers two distinct acceptations in Geography:
  A classical acceptation synonym of concentration of matter and energy. Polarisation is the attraction exerted by a place on a more or less extended and heterogeneous space that is in a situation of dependency with respect to this centre. Space is compared to a magnetic field in which a place, assimilated to a pole (generally a city or a region) exerts a magnetisation proportional to its population, to its activities (...)

• Central places theory
  13 October 2004, by D. P.

  The central places theory was conceived, primarily by W. Christaller and A. Lösch, in order to explain size and number of cities and their spacing in a territory. It relies on a definition of city that considers it essentially as a distribution centre of goods and services to a scattered population, and on optimisation principles (which take transport costs into account). This theory stands on the limit between geography and spatial economy, and may be claimed by both disciplines. The (...)

• Friction
  6 October 2004, by D. P.

  Friction of distance is an expression that is sometimes used in order to designate the attenuating effect of distance on intensity of interactions between places, or else, in gravity models, the parameter measuring this gradient.