isarithmic

Isarithmic is an adjective related to isarithms, lines that connect points of equal value on a map or other spatial field. In cartography and data visualization, isarithmic mapping (also called isopleth mapping) depicts a continuous phenomenon by drawing isolines that join areas with the same value. The term is typically used as an alternative to isoline or isopleth, and its spelling varies little across sources.

Construction and interpretation: A dataset consisting of discrete sample points is used to estimate values across a region. Interpolation methods such as inverse distance weighting, kriging, or spline interpolation generate a continuous surface, from which lines of constant value are drawn at chosen intervals. When combined with shading or color, an isarithmic map communicates gradients and patterns more intuitively than point symbols alone.

Applications: Isarithmic maps are common in meteorology (isotherms for temperature, isobars for pressure), oceanography, hydrology, and geology. They are also used in environmental science and urban planning to visualize gradients of elevation, rainfall, or pollution concentration.

Limitations: The choice of interpolation method, sampling density, and interval spacing can influence the appearance and perceived significance of features. Misleading contours can arise in areas with sparse data or abrupt changes, so developers typically accompany isarithmic maps with metadata and uncertainty notes.

See also: Isoline, isopleth, contour line, contour map, interpolation, GIS.