Contour line - Definition and Overview

Contour map

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 (http://avc.comm.nsdlib.org/cgi-bin/wiki_print.pl?Drawing_Contour_Plots). A lesson plan that deals with drawing various isopleths.
• See also Forthright's Phrontistery (http://phrontistery.50megs.com/contour.html) for many more different types of isopleths.