Isopleth maps connect points of equal value through isolines to show variations and distributions of elements. Values can represent quantities, intensities or densities and common examples include isobars (equal pressure), isotherms (equal temperature), and isohyets (equal precipitation). Isopleth maps are constructed by marking data points, determining suitable interval values, joining equal points with smooth lines, and adding a key. They have various applications in climatology, demography, and showing altitude or terrain. Merits include scientific accuracy while demerits can include inaccuracies from interpolation of many data points.

1. Subhasish SutradharClassNote
Concept and utility of Isopleth Map
Isopleth: The term isopleth has been derived from greek word isos meaning same
and plethron meaning measure . Thus isopleths are lines joining places of equal value.This
value may be in the form of quantity, intensity or density. Following are few examples of
isopleths-
Isallobar: A line representing points of equal atmospheric pressure change.
Isallodrosotherm: A line representing points of equal dew point temperature change.
Isallohypse: A line representing points of equal height change for a pressure surface.
Isallotherm: A line representing points of equal atmospheric temperature change.
Isentrope:A line representing points of equal potential temperature.
Isoabnormal: A line representing points of equal anomalies of an atmospheric variable
Isobar: A line representing points of equal atmospheric pressure
Isobath: A line representing points of equal depth under water
Isobathytherm: A line representing depths of water with equal temperature
Isobrunt: A line representing points of equal thunderstorm activity.
Isoceraunic: A line representing points of equal number of thunderstorm days. (also spelled
isokeraunic)
Isochasm: A line representing points of equal recurrence of auroras
Isocheim: A line representing points of equal mean winter temperature
Isochrone: A line representing points of equal time-distance from a point, such as the transportation
time from a particular point
Isodapane: A line representing points of equal transport costs for products from production to
markets
Isodop: A line representing points of equal doppler radar velocity.
Isodose: A line representing points of equal intensity of radiation
Isodrosotherm: A line representing points of equal dew point
Isogeotherm: A line representing points of equal mean temperature
Isogloss: A line separating linguistic features
Isogon: A line representing points of equal angle or direction.
Isogonal: A line representing points of equal magnetic declination
Isohaline: A line representing points of equal salinity in the ocean
Isohel: A line representing points receiving equal amounts of sunshine
Isohume: A line representing points of equal humidity
Isohyet: A line representing points of equal precipitation
Isohypse: A line representing points of equal altitude in the atmosphere especially a pressure surface.
Isoneph: A line representing points of equal amounts of cloud cover
Isopach: A line representing points of equal atmospheric thickness.
Isopectic: A line representing points where ice begins to form at the same time each fall or winter
Isophene: A line representing points where biological events occur at the same time, such as crops
flowering
Isoplat: A line representing points of equal acidity, as in acid precipitation
Isopor: A line representing points of equal annual change in magnetic declination
Isopycnic: A line representing points of equal atmospheric debnsity.
Isostere: A line representing points of equal atmospheric specific volume.
Isotac: A line representing points where ice begins to melt at the same time each spring
Isotach: A line representing points of equal wind speed
Isothere: A line representing points of equal mean summer temperature
Isotherm: A line representing points of equal temperature
Isotim: A line representing points of equal transport costs from the source of a raw material

2. Subhasish SutradharClassNote
Methods of Construction (Procedures):
1. Mark on the base map your observed values. Values should be located accurately at the
exactly position you collected the data or value, locate as more points of value as you can to
make accuracy at the end result.
2. Decide the suitable value or number for the isolines by looking the range you have
collected. Here, you work out on how many lines will fit properly on the map between your
maximum for and minimum values, but making a fixed interval is most important.
3. Join all places or points of equal value with smooth line in accordance to the interval you
have chosen. It is necessary to determine the values of intermediate points through which the
Isoline will pass using “logical interpolation”.
4. Check the accuracy of the construction quickly to see if there is no point omitted.
5. Show the key appropriate. And title to assist interpretation. Note, always a key used when
different shades or color has been used.
Applications of Isopleth Maps:
Isopleth maps used in different fields to show the equality of values. The following are
some of Isoline map’s applications,
1. Isopleth maps used in climatic data to show areas with the same temperature, pressure,
rainfalls etc.
2. Used in population or production data to show similarities between one area and another.
3. Used in showing altitude with the same height`s meters by using contour lines between one
area and another.
 Merits of Isopleth Technique:
1. Isopleth are more scientific than other methods of showing distribution and
effectively show the distribution and variations.
2. This is especially useful for climatic maps such as isobars, isotherms , isohyet etc.and
is known as the main tool for the meteorologists.
3. It is very easy to determine the gradient (rate of change )with the help of isopleth
maps.
4. When isopleth are wide apart ,they show low gradient but when they are
closer together they show high gradient.
5. Isopleth lines are independent of political boundaries and best suitet to show the
natural pattern of distribution of an element.
6. Isopleth is the most suited method for showing elements having transitional values
,this is a reason that isopleth are invariably used to show the distribution of
temperature ,pressure and other climatic elements.
 Demerits of Isopleth Technique :
1. Many isopleths are drawn by interpolation which sometimes lead to inaccuracy in the
directions of isopleths and the pattern of distribution shown by those lines is distorted.
2. It is confusing when there is large list of points or dots.
3. It is time consuming when there is large number of dots or points.