# isopleth

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## isopleth

isopleth (īˈsəplĕthˌ), line drawn on a map through all points of equal value of some measurable quantity. In many meteorologic, oceanographic, or geologic studies some physical or chemical property is examined that varies from place to place on a map. Isopleths showing the quantity of the property being studied can be drawn on the map to highlight regional trends of high or low abundance of that property. For example, topographic maps showing contours of equal elevation are probably the most common type of isopleth maps. Relief “highs” (hills) are shown by concentric contour isopleths, and depressions such as volcanic craters are shown by concentric contours with hachures pointing toward the center of the depression. Isopleths are drawn on weather maps to indicate lines of equal air pressure (isobars) and equal temperature (isotherms). Isobaths are lines connecting points of equal depth in lakes and oceans. Isopach maps show distribution of thickness of a given rock unit. Gravity maps are drawn showing isogals (lines of equal gravitational acceleration). Variations in the strength of the earth's magnetic field are shown by isogams (after gamma, the common unit for measuring magnetic strength).

## isopleth

[′ī·sə‚pleth]
(mathematics)
The straight line which cuts the three scales of a nomograph at values satisfying some equation. Also known as index line.
(meteorology)
A line of equal or constant value of a given quantity with respect to either space or time. Also known as isogram.
More specifically, a line drawn through points on a graph at which a given quantity has the same numerical value (or occurs with the same frequency) as a function of the two coordinate variables. Also known as isarithm.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## isopleth

On a chart or a graph, a line of constant value of a given quantity with respect to either space or time. Also called an isogram.
References in periodicals archive ?
Each grid consisted of 701 X 301 grid nodes providing reasonable resolution for generation of the isopleth maps.
Isopleths of abundance (kg km-[lineal.sup.-1]) of Heterocarpus reedi estimated in surveys using swept area method by depth, latitude, and year.
Different types of thematic maps, such as chloropleth or isopleth, will be discussed, along with their use for displaying data visually.
Second, these summary data are entered into the SURFER computer program to generate isopleth contours.
Areas occupied by wolf packs (80% isopleth of harmonic mean) had average road densities of 0.23 km/k[m.sup.2] (Table 1).
Figure 3 gives isopleth diagrams comparing the effects of ozone level with those of DOC (3a, b) and CDOM (3c, d).
We used the P = 0.05 level as a convenient isopleth indicating which male traits contributed most to female preferences and not as an absolute indicator of whether or not the trait was used in female preferences.
Its omitted 1969 isopleth would pass southeast from Pasadena to La Habra, northeast to Pomona, and thence further eastward to Riverside and Redlands.
A contamination isopleth was imposed on the groundwater flow map showed that saturated groundwater flow was not responsible for plume geometry and spread.
For each day and night, multiple unique polygons were created by each 75% isopleth; each polygon reflecting a peak in location density where a moose bedded.
We used the 50-percent isopleth of the 80 m UD to identify home range cores.

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