Isochrone map

An isochrone map (isochrone plan, isochrone diagram) in science and urban planning is a map showing areas related to between different points. An isochrone is defined as "a line drawn on a map connecting points at which something occurs or arrives at the same time". Such a map is sometimes termed simply an isochrone. In hydrology and transportation planning isochrone maps are commonly used to depict areas of equal travel time. The term is also used in cardiology as a tool to visually detect abnormalities using body surface distribution.

Isochrone maps have been used in transportation planning since 1887 or earlier. Early examples of Isochrone maps include the Galton´s Isochronic Postal Charts and Isochronic Passage Charts of 1881 and 1882,Bartholomew's Isochronic Distance Map and Chart first published 1889 or earlier and Albrecht Penck's Isochronenkarte first published 1887. Where as Galton and the Bartholomews published maps depicting the days or weeks it took to travel long distances, Albrecht further developed the idea to not only depict long distances and world travel but also smaller areas. Penck also created a series of maps that only depict the travel times of a certain transportation mode, for example Rail transport. Isochrone maps are commonly used in the UK in connection with development control.Information technology in the 21st century has enabled them to be dynamically generated for use in websites, being used by house hunters wishing to evaluate residential areas.

Isochrone and related maps are used to show the time taken for runoff water within a drainage basin to reach a lake, reservoir or outlet, assuming constant and uniform effective rainfall. An early example of this method was demonstrated by Clark in 1945.

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