Mapping techniques

Some data is easier to understand when it is shown on a map. This is especially true of spatial data, where the spread of the information is important.

Choropleth maps

Choropleth maps show interval data (data that is linked, rather than data from different categories) as colours. They are shaded in using one colour, where the darker shades represent high numbers and the lighter shades represent low numbers. A choropleth map needs a key to explain what the different shades mean. Population density can be shown using a choropleth map.

A choropleth map shows global population densities by colouring in similar areas in the same colour and pattern. A key explains what each colour means.

Isoline maps

Isoline maps show lines that join up areas or values that are equal. Atmospheric pressure is shown using an isoline map. The areas of equal pressure are joined using a line, which helps people to see the position of high and low-pressure systems.

An isoline map uses lines to show areas of similar value. If the lines are closer together, values are changing rapidly. An example is a weather map with isobars.

Dot maps

Dot maps show information as individual dots on a map. Each dot might represent more than one of something. Dot maps are often used to show population distribution.

A dot map uses dots to represent a certain number of people. A key explains how many people each dot represents, eg 1 dot = 100,000 people.

Desire lines and flow lines

Desire and flow line maps show movements from one place to another:

  • flow lines show the exact path of movement
  • desire lines show a general direction of movement

Movements are shown as lines. Thick lines show high amounts of movement and thin lines show low amounts. Trade or migration patterns are often shown using desire or flow lines.

A desire line map uses lines to show migration of people between countries.World trade patterns shown using desire lines

Proportional symbols

Proportional symbols can be added to a map to show differences between places. The same symbol appears larger or smaller, depending on how something changes. Proportional symbols on maps could be used to show the number of wind farms within a country.

A proportional symbol map uses size of shapes to compare data, eg wind energy locations across the UK with size of each circle corresponding to the amount of electricity generated.