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