Mapping techniques

Some data is easier to understand when it is shown on a map. This is especially true of spatial data, where 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 showing population density.

The world map above shows us that the most densely populated areas are western Europe, the north-east of the USA and coastal areas in eastern Asia such as China. The least populated areas (shown in yellow) are across the polar regions, through South America and central parts of Australia. North Africa and the Middle East are also sparsely populated regions of the world.

Isoline maps or synoptic charts

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.

The isoline map above shows there is a ridge of high pressure over northern Italy and a trough of low pressure off the coast of Scotland.

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.

Within the dot map it is possible to determine that most people live in western Europe, the north-east of the USA, and coastal areas in eastern Asia such as China. The least populated areas (shown in yellow) are across the polar regions, through South America and central parts of Australia and Asia.

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.

Interpreting the flow line map tells us that migrants to Britain come form three locations directly, the Caribbean, Uganda and India/Pakistan. It also tells us that people from the UK migrate to South Africa, Australia and New Zealand, and that these people travel furthest.

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.Wind energy locations across the UK, with size of each circle corresponding to the amount of electricity generated

The single location which generates the most energy is off the eastern coast of Norfolk, England. However, there are multiple locations across Scotland which collectively produce the most electricity within the UK.

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