Adding other information to maps

Coloured circles of varying diameter can effectively describe the geographic distribution of some measurements. Other simple displays such as pie or bar charts can also be superimposed on the regions of a map, but they must be simple to be effective.

If the information about each region is complex, ordinary tables and graphs may convey it better than a map.


Urban and rural population in Africa

Pie charts have been added to the map of Africa below. The area of each circle represents the total population in 2006 and the pie slices show the proportions who are classified as urban and rural.

An alternative display would have been solid circles whose colour represented the proportion of urban dwellers, but the pie charts let you estimate more accurately the proportion in any country.

People with AIDS/HIV in Africa

The next map shows the number of people with AIDS/HIV in each country in 2005 (circle area) and also the proportions of these who are children, adult women and adult men. (A question mark represents unavailable information.)

This map conveys the information well, but a similar diagram would become much harder to understand if there were more than three categories.

Other examples

The following three maps were published in the Contemporary Atlas of New Zealand. In each case, bar charts or stacked bar charts are superimposed on different regions.

The above diagram describes submissions about management of forests in the West Coast of New Zealand. The bar charts successfully convey the information that a larger proportion were in favour of sustainable logging in the West Coast than elsewhere in New Zealand. (The West Coast had high unemployment and logging provided jobs.)

The bar charts here again show clearly that a larger proportion of companies in New Zealand were foreign-owned in Auckland and Wellington than those in the rest of the country. It also shows the increase in companies based in Auckland rather than Wellington and the increasing proportion of foreign-owned companies in Auckland in 1997. However the rotation of the map and the 3-dimensional bars do not make it clearer.

The final map tries to display too much information in its stacked bar charts. Their areas reflects the land areas planted in vegetables (a size measurement) and the slices represent the proportions of land devoted to different vegetables.

If bar or pie charts are added to a map, they should be simple.