What Are Isopleth Maps? Applications of  Isopleth Maps

What Are Isopleth Maps

What Are Isopleth Maps?

An Isopleth map is a map that employs lines or colors to identify places with comparable regional characteristics. Isopleth maps condense information about a region by displaying areas with a continuous distribution.

Lines on isopleth maps can be used to show areas with the same elevation, temperature, rainfall, or other characteristic; values between lines can be interpolated.

Color may also be used in isopleths to depict regions where some quality is the same; for example, a map that uses colors ranging from red to blue to indicate temperature ranges.

An isopleth varies from a choropleth in that its lines or regions are established by data rather than by a designated territory, such as a political unit.

This sort of map is good for demonstrating progressive development over time and avoids the sudden shifts produced by boundary lines on choropleth maps.

Temperature, for example, is a phenomenon that should be mapped using isoplething since it exists at every place (is continuous), yet it does not change abruptly at any point (like population density may do as you cross into another census zone).

For this reason, relief maps should always be in isopleth form.

These maps can be of two types:

  • Lines of equal value are drawn so that all values on one side are greater than the “isoline” value and all values on the other side are lower, or
  • Ranges of comparable value are filled with colors or patterns that are similar.

Isopleth Map Construction Methods

We need a base map of the area with point data to create isopleth maps (showing values). All of the points for which data is available must be plotted on the map.


  1. Draw your observed values on the basic map. Values should be precisely found at the exact position where the data or value was obtained; find as many points of value as possible to ensure accuracy in the ultimate result.
  2. Examine the range you’ve gathered to determine the appropriate value or number for the isolines. Here, you calculate how many lines will fit properly on the map between your maximum for and minimum values, but the most important thing is to make a constant interval.
  3. Use a smooth line to connect all places or points of equal value based on the interval you’ve set. Using “logical interpolation,” the values of intermediate sites through which the Isoline will pass must be determined.
  4. Quickly check the accuracy of the construction to ensure that no points have been omitted.
  5. Display the proper key. And a title to help with interpretation. When several hues or colors are employed, a key is always used.

Types of isopleth maps

The types are:

  1. Isohyete map (rainfall)- The map shows the lines of equal rainfall amounts. The color and pattern of the regions with the same amount of rain, which is useful to see the region where large amounts of rain occur.

The isohyete method uses lines or patterns to represent areas having a common value. The basis for isohyet is to draw a line around each area of identical value that can be seen on your map.

This line divides each region into two halves: one higher than the line and one lower than it.

  1. Isotherm map. (temperature) – The map is divided into regions having the same measured, or observed, temperature. The region of equal temperature will have a common color on the map, with values every 5°F or so.
  2. Isobars maps. (Air pressure) – The map is divided into regions having the same air pressure. The air pressure -p, which is the pressure at a particular point in atmosphere measured in millibars (the unit used for measuring average atmospheric pressure).

The highest and lowest points of value are marked on the map, with points between them determined by interpolation.

  1. Isohels maps. (sunshine) – The map is divided into regions having the same amount of sunshine. The regions with equal number of hours of daylight will have a common color on the map, with values every 12° in each region.

The isopleth method provides a way to compare variants of one topic, such as average earnings within an industry. This can be done by plotting points that are worth the same amount and identifying the values of these points.

  1. Contours map (height) – This type of map depicts the lines of equal height. The within each contour line (in the map) there are values that are twice as high or twice as low as the contour above or below it.

Applications of  Isopleth Maps

Isopleth maps are used in a variety of fields to demonstrate value equality. The applications of Isoline map are as follows.

  1. In climatic data, isopleth maps are used to illustrate areas with the same temperature, pressure, rainfall, and so on.
  2. Used in demographic or production data to demonstrate similarities between two areas.
  3. Used to display altitude with the same height’s meters by employing contour lines between two areas.
  4. In the topographical maps, isopleth maps are used to show areas with the same height

and depth in land.

  1. They are also used to represent areas that have a common value such as weight, money or distance by using similar contour lines.
  2. Isopleth maps are used to show areas that have a common trait with a choropleth map by using similar contours or color patterns between two areas.

Merits of Isopleth Technique

The merits include:

  1. Isopleths are more scientific than other techniques of displaying distribution because they efficiently depict the distribution and variations.
  2. This is useful as the main tool for meteorologists and is especially important for climatic maps such as isobars, isotherms, isohyet, and so on.
  3. Isopleth maps make determining the gradient (pace of change) relatively simple.
  4. When isopleths are far apart, the gradient is moderate, but when they are near together, the gradient is steep.
  5. Isopleth lines are unaffected by political boundaries and are best suited to depict an element’s natural pattern of distribution.
  6. Isopleth is the best approach for depicting elements with transitional values, which is why isopleth is generally used to depict the distribution of temperature, pressure, and other climatic factors.
  7. Good for showing the pattern of distribution in a region.
  8. In general, isopleth technique is easy to interpret because the scale and measure are already shown, so it’s easy to learn how to read them.
  9. It is best suited for the display of large amount of data and if they are displayed together, they can be compared quickly and clearly.
  10. Better way to see change in value over a region using contours or dots on maps or graphs based on them.

Demerits of Isopleth Technique

They are:

  1. The more contour lines, the more difficult it is to read the image.
  2. Isopleth map relies on interpolation and estimating, after a certain period of time this technique loses its desired accuracy.
  3. If it is used to show large varieties of data on maps, it can be hard to read quickly because of their large amount of data in a small space.
  4. If the data is not correctly represented then it can be hard to compare them because this technique shows how a quantity changes with distance or within an area.
  5. When comparing data on two maps, you need to decide how to compare them because the gradients are different in two areas.
  6. The biggest demerits of the isopleth technique is that it can’t represent numbers very accurately and if there is no calibration, the values will be inaccurate.

Choosing the Interval of Isopleth

Choosing an Isopleth Interval Isopleths are drawn at a defined interval, i.e., the interval between all Isopleth lines should be the same.

The location of an isopleth on a map reveals the gradient, i.e., if the isopleths on a map are close to one another, the gradient is steep.

When the isopleths are far apart, on the other hand, the gradient is gentle. As a result, the isopleth interval should be chosen with care.

Rules to follow while deciding on an isopleth interval

  1. Determine the map’s minimum and maximum values.
  2. Determine the value’s range, i.e., Range = maximum – minimum value.
  3. Determine the interval in which number, such as 5,10,15, and so on, based on the range.
  4. The exact point at which an isopleth is drawn is calculated using the following formulae.

 Isopleth Maps FAQs

What is an isopleth?

An isoline on a graph depicting the occurrence or frequency of a phenomenon as a function of two factors. Or a line on a map linking sites where a given variable has a constant value.

What is an isoline on a map?

Isolines are lines drawn on a map that connect data points of the same value. Contour lines, for example, depict relief and connect locations on a map that are the same height.

Isobars, on the other hand, show pressure bands of high and low pressure and connect points with the same atmospheric pressure.

What is the most common Isoline map?

An isoline drawn between points with the same elevation above sea level is a contour line, which you see on maps all the time and is the one you’d have to utilize the most.

Another type of isoline is an isobar, which connects locations with the same atmospheric pressure as depicted on weather maps.

Which places are joined by the lines used in the isopleth maps?

Isopleths are lines painted on weather maps to denote lines of equal air pressure (isobars) and equal temperature (isotherms). Isobaths are lines that connect places of equal depth in lakes and oceans.

Is isopleth and isoline the same?

Isopleth is a line drawn on a map across all points with the same value of some measurable variable, whereas isoline is any of numerous types of line on a map, chart, or graph that connects points with the same value of a parameter.

What is an isoline example?

A constant-value line on a map or graphic. Isobar (equal barometric pressure), isotherm (equal temperature), and isohyet are some examples (equal precipitation).

What does ISO mean in geography?

Because the prefix ‘iso’ is derived from the Greek word for equal, an isoline must be a line connecting equal locations.

A contour, for example, is a line drawn on a map that connects all areas that have the same height above sea level. Contour lines are isolines that connect locations with the same height value.

How do you make an isopleth map?

Join point A of 10°C temperature with point B of 4°C temperature for this aim. Divide the line AB into 10 – 4 = 6 equal segments and count five divisions from A or one division from B to get the point with a temperature of 5°C.

A curving line connects all three sites with temperatures of 5°C.

Is a topographic map an isoline map?

Maps that depict lines connecting locations of equal value. (A topographic map, for example, is an isoline map in which lines connect locations of equal elevation.)

What is isopleth phase diagram?

In a temperature-composition diagram, an isopleth* is a line of constant composition that runs parallel to the temperature axis. The critical temperatures are typically an infinitesimal amount above and below the temperature of each phase change.

What is interval between each isopleth?

Isopleths are drawn at a constant interval, i.e., the interval between all Isopleth lines should be the same.

The location of an isopleth on a map indicates gradient, i.e., when the isopleths on a map are close to one another, the gradient is steep. When the isopleths are separated, the gradient is mild.

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