Isopleter

Isopleter is a historical term used in cartography and the geosciences to denote either a line on a map connecting points of equal value of a variable or the device or method used to construct such lines. In many old publications the isopleter and isopleth are used interchangeably, though later usage tends to standardize on isopleth (also called a contour line) for the line and to reserve isopleter for the instrument or technique that creates lines.

Origin and usage: The word derives from Greek roots iso- meaning "equal" and pleth- meaning "quantity" or "value," conveying the idea of equal quantities along a line. The concept dates to early mapmakers who sought to visualize spatial variation of variables such as temperature, precipitation, or mineral concentrations. Isopleters appeared both as manual drawing tools and as theoretical constructs in statistical visualization.

Modern status: The term isopleter is largely obsolete in current scholarly usage. Contemporary texts prefer isopleth or contour line for the lines themselves, and digital cartography often uses isopleth mapping or more specialized terms for the variable (such as isotherm for temperature, isobar for pressure).

See also: isopleth, contour line, isoline, isarithm.