# What Are Isolines?

## Isolines are used to illustrate data on maps more effectively

Topographic maps use a wide variety of symbols to represent human and physical features, including isolines, which are often used on maps to represent points of equal value.

## The Basics of Isolines and Contour Lines

Isolines, also referred to as contour lines, can be used to represent elevation on a map by connecting points of equal elevation, for instance. These imaginary lines provide a good visual representation of the terrain. As with all isolines, when contour lines lie close together, they represent a steep slope; lines far apart represent a gradual slope.

But isolines can also be used to show other variables on a map besides terrain, and in other themes of study. For example, the first map of Paris used isolines to depict population distribution in that city, rather than physical geography. Maps using isolines and their variations have been used by astronomer Edmond Halley (of Halley's comet) and by doctor John Snow to better understand an 1854 cholera epidemic in England.

This is a list of some common (as well as obscure) types of isolines used on maps to represent different features of the terrain, such as elevation and atmosphere, distances, magnetism and other visual representations not easily shown on a two-dimensional depiction. The prefix "iso-" means "equal."

## 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.

## 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.

## 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.

## 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.

## Isoneph

A line representing points of equal amounts of cloud cover.

## 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.

## Isopleth

A line representing points of equal numerical value, such as population.

## Isopor

A line representing points of equal annual change in magnetic declination.

## Isostere

A line representing points of equal atmospheric density.

## 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.