<P> An isodynamic line (from δύναμις or dynamis meaning' power') connects points with the same intensity of magnetic force . </P> <P> Besides ocean depth, oceanographers use contour to describe diffuse variable phenomena much as meteorologists do with atmospheric phenomena . In particular, isobathytherms are lines showing depths of water with equal temperature, isohalines show lines of equal ocean salinity, and Isopycnals are surfaces of equal water density . </P> <P> Various geological data are rendered as contour maps in structural geology, sedimentology, stratigraphy and economic geology . Contour maps are used to show the below ground surface of geologic strata, fault surfaces (especially low angle thrust faults) and unconformities . Isopach maps use isopachs (lines of equal thickness) to illustrate variations in thickness of geologic units . </P> <P> In discussing pollution, density maps can be very useful in indicating sources and areas of greatest contamination . Contour maps are especially useful for diffuse forms or scales of pollution . Acid precipitation is indicated on maps with isoplats . Some of the most widespread applications of environmental science contour maps involve mapping of environmental noise (where lines of equal sound pressure level are denoted isobels), air pollution, soil contamination, thermal pollution and groundwater contamination . By contour planting and contour ploughing, the rate of water runoff and thus soil erosion can be substantially reduced; this is especially important in riparian zones . </P>

Contour line on map connecting points of equal stratigraphic thickness