Distribution maps

Distribution maps

1. Distribution Maps

2. 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.

3. Types of distribution map
Dots map
Choropleth map
Proportional Circles map

4. Dot distribution map
Dot Distribution maps count on the use of dots to
represent a “value” of an area.
Also known as dot density maps
This 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.

6. Advantages of Dot Distribution Maps
easy to understand
show the varying density of a phenomena
dot 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

7. 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.

8. 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?

9. 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 scale
Sometimes more than one variant can be
represented on the distribution map.
Eg: HDI rank vs Colonial control

10. HDI (2002)

11. No Access to Safe Water Map

12. World Life Expectancy Map

13. 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.

14. 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.

15. 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.

19. 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.

20. 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

21. 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

22. 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.

25. 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).

26. Disadvantages of isopleth maps:
•
They are not suited for showing
discontinuous or 'patchy' distributions
• A large amount of data is required for
accurate drawing.

27. 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)