Distribution Maps

Uses of Distribution Map

It provides an easy way to visualize how a measurement varies across an area.

Disadvantages: can be difficult to distinguish between different shades in the maps.

Types of distribution map

Dots mapChoropleth mapProportional Circles map

Dot distribution map

Dot Distribution maps count on the use of dots to represent a “value” of an area. 

Also known as dot density mapsThis example shows the population

distribution of Australia.  In this map, one dot is equal to 1000 people;

we can see where population is at its highest and lowest quite easily.

Advantages of Dot Distribution Mapseasy to understand show the varying density of a phenomenadot placement: placement of dots takes

into account the distribution of other phenomena: a dot map of crop acreage would not place dots in urban areas, a dot map of population would cluster dots near urban areas, etc. Therefore, patterns are meaningful.

Allows for mapping with another distribution of some other phenomena: e.g. use multi-colored dots, or use dot maps over choropleth map. Therefore, they are good for complex maps

Disadvantages of Dot Distribution Maps• There is a human tendency to underestimate density and it’s easy to do with this map

•If dots get too dense, it is difficult to read

•Dot placement: computer placement of dots is often random; thus, patterns are often not meaningful if the map is misleading.

Dot Distribution Maps

•If not created properly, these maps, and other maps, can be confusing.

•In the map you will see, dots were placed randomly to identify alligator populations in the countries of North America What does the map you will see imply?

Choropleth Map

Some distribution map uses different shades of a single colour or a range of colours to show the intensity of a variant.

Eg: HDI scaleSometimes more than one variant can be

represented on the distribution map.Eg: HDI rank vs Colonial control

HDI (2002)

No Access to Safe Water Map

World Life Expectancy Map

Advantages of Choropleth Maps

•It provides an easy way to visualize how a measurement varies across an area.

•When defining regions is important to a discussion (as in an election map divided by electoral regions), choropleths are preferred.

•Choropleth maps are also appropriate for indicating differences in land use, like the amount of recreational land or type of forest cover.

Disadvantages of Choropleth Maps•They give a false impression of abrupt change at the boundaries of shaded units.

•It can be difficult to distinguish between different shades in the maps.

Distribution map (Proportional Circles)

Distribution maps can also be represented by circles.

A scale of proportional circle is shown in the legend.

Candidates have to compare the size of the circles against the legend.

A good visual representation of numbers is shown with the proportional circles.

Sometimes more than one variant can be shown with the use of pie charts as the circles.

In this proportional circle map of western Europe the circles are divided into percentages displaying the age structures. Proportional circle maps are good maps to use when you have different variables representing different information.

Advantages of proportional symbol maps:

•They show data occurring at points •They show absolute values (precise numbers)•The circles can be subdivided to show percentages of the whole •They are easy to make

Disadvantages of Graduated Symbol Maps:

•Densities/ratios/rates are hard to show with this map

•It’s hard to tell the relationship between the different circle sizes

Isoline/Isopleth Maps

These maps are used to show quantities that vary smoothly over the earth’s surface.These maps can take two forms: 1. Lines of equal value (“iso” means equal) or 2. Ranges of similar value are filled with similar colors or patterns.

Advantages of Isoline Maps

• Good for showing gradual change over space

• They avoid the sudden changes which boundary lines produce on choropleth maps. Temperature, for example, is something that should be mapped using isopleth maps, since temperature exists at every point (is continuous), yet does not change abruptly at any point (like population density may do as you cross into another census zone).

Disadvantages of isopleth maps:

• They are not suited for showing discontinuous or 'patchy' distributions

• A large amount of data is required for accurate drawing.

How to answer distribution map questions

Step 1: State the general relationship between the variants.

Step 2: Use general examples of regions to support the relationship.

Step 3: Use specific examples of countries/towns to further describe the relationship.

(For higher marks Qn)