The Terminology of Certain Map Symbols

A LTHOUGH many cartographic terms, such as contour isotherm, and hypsometric tint, have acquired more or less standard meanings, there are no generally recognized terms for other, equally important types of symbol or for the various larger categories into which map may be classified. This leads to confusion and circumlocution. The American Geographical Society hopes to adopt in its own publications at a later date a consistent usage with regard to a few of these terms, in the belief that this may help establish greater consistency elsewhere. First, however, the comments of geographers and cartographers are invited upon the following tentative scheme. On the chart on page 650 of this number of the Geographical Review several of the proposed terms are used. The present note deals solely with the terms for classified on the chart as quantitative, specifically with uniform line symbols and symbols. As an all-embracing generic term for any and all lines on maps indicating constant values a number of words have been invented and employed by different writers; for example, isopleth, isarithm, iso-line, isogram, isontic isometric line.' It is proposed that isogram, which means line, be the term adopted for this purpose, with permissive use of the Greek-English hybrid iso-line as an alternative. For the two principal classes of isogram, the terms isometric line and isopleth are proposed, an isometric line being a line that represents a constant value or intensity pertaining to every point through which it passes (for example, contour isotherm, isobar), and an isopleth being a line that represents a quantity, assumed to be constant, pertaining to certain specified areas through which it passes (for example, lines showing equal densities of population or equal birth rates). For different kinds of isograms a large number of specific terms beginning with isohave gained currency. For areal there is no corresponding terminology. Quantitative areal symbols are those that, by differences in color, tone, or intensity of design, indicate differences in quantity that pertain to or are assumed to pertain to the several areas covered by the symbols, each symbol constituting one element in an pattern. It is suggested that chorogram (on the analogy of isogram) be adopted as a generic term for any and all quantitative areal and that other terms beginning with choror choro(meaning area, place) be employed for particular types of chorogram. For the two principal categories of chorogram, the terms choropleth and chorisogram are proposed. The distinction is inherent in the nature of the lines that define the areas covered by of each type. Choropleth has already gained some currency as the designation for an areal symbol bounded by the limits of political or other statistical subdivisions of the territory mapped.2 Each choropleth indicates a quantity or range of quantities that pertains directly to one or more of such subdivisions. A chorisogram would be an areal sym

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• Error on Choroplethic Maps

  George F Jenks, FRED C CASPALL•Annals of the Association of…•1971

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