|
A cartogram is a map in which some thematic mapping variable – such as travel time, population, or Gross National Product – is substituted for land area or distance. The geometry or space of the map is distorted in order to convey the information of this alternate variable. There are two main types of cartograms: area and distance cartograms. Cartograms have a fairly long history, with examples from the mid-1800s. == Area cartograms == An area cartogram is sometimes referred to as a ''value-by-area map'' or an ''isodemographic map'', the latter particularly for a ''population cartogram'', which illustrates the relative sizes of the populations of the countries of the world by scaling the area of each country in proportion to its population; the shape and relative location of each country is retained to as large an extent as possible, but inevitably a large amount of distortion results. Other synonyms in use are ''anamorphic map'', ''density-equalizing map'' and ''Gastner map''.〔(Gallery of Data Visualization - Bright Ideas )〕〔(UNEP GRID Ardenal: Anamorphic Maps )〕 Area cartograms may be contiguous or noncontiguous. The area cartograms shown on this page are all contiguous, while a good example of a noncontiguous cartogram was published in (''The New York Times'' ). The online resource (SHOW® ), provided by (Mapping Worlds ), creates discontiguous cartograms for different geographies (United States, Japan and World at this time) interactively, allowing users to quickly compare various characteristics. This method of cartogram creation is sometimes referred to as ''the projector method'' or ''scaled-down regions''. Cartograms may be classified also by the properties of shape and topology preservation. Classical area cartograms (shown on this page) are typically distorting the shape of spatial units to some degree, but they are strict at preserving correct neighborhood relationships between them. Scaled-down cartograms (from the NY Times example) are strictly shape-preserving. Another branch of cartograms introduced by Dorling, replaces actual shapes with circles scaled according to the mapped feature. Circles are distributed to resemble the original topology. Demers cartogram is a variation of Dorling cartogram, but it uses rectangles instead of circles, and attempts to retain visual cues at the expense of minimum distance. Schematic maps based on quad trees can be seen as non shape-preserving cartograms with some degree of neighborhood preservation. A collection of about 700 contiguous area cartograms is available at Worldmapper,〔(Worldmapper:The world as you've never seen it before )〕 a collaborative team of researchers at the Universities of Sheffield and Michigan. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cartogram」の詳細全文を読む スポンサード リンク
|