Contour line

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A '''contour line''' (also '''isopleth''', '''level set''', '''isogram''' or '''isarithm''') for a function of two variables is a curve connecting points where the function has a particular value. A '''contour map''' is a map showing contour lines. The gradient of the function is always perpendicular to the contour lines. When the lines are close together the gradient is large: the variation is steep. Different types of contour lines are given different names according to the nature of the quantity involved: * elevation: contour lines on a topographic map * pressure: isobar. * temperature: isotherm. * dew point: isodrosotherm. * humidity: isohume. * wind speed: isotach. * wind direction: isogon. * liquid precipitation amount: isohyet. * economic production: isoquant. * presence of linguistic feature: isogloss "Iso" can be replaced with "isallo" to give it the meaning of a line connecting points where some variable has changed at the same rate during some time period. ==External links== * ''Drawing Contour Plots''. A lesson plan that deals with drawing various isopleths. * See also ''Forthright's Phrontistery'' for many more different types of isopleths.de:Isolinie es:is�grama ja:等高線 sl:Izo-črte