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Thematic Mapping
&
Data Classification
Thematic Mapping & Data
Classification
Objectives: What is a thematic map
Qualitative vs. Quantitative
Data types
How do we map this data?
Considerations
What is a Thematic Map?
Definition: “A map designed to demonstrate
particular features or concepts.”
In other words, a thematic map presents a
graphic theme about a subject.
Most maps you create are thematic maps! It is
not a reference map nor is it a topographic
map because it only displays one theme.
Types of Thematic Maps
Thematic maps can be divided into two groups:
1. Qualitative thematic maps: these show the spatial
distribution or location of kind. For example, a map
representing the spatial distribution of earthquakes.
Qualitative maps use nominal data:
The most basic form of measurement. It is just a label,
category or name. There is not much information you can
derive from nominal data. Mainly just distribution and/or
location of a phenomenon.
For example: The distribution of earthquakes
Types of Thematic Maps
2. Quantitative Thematic Maps: Display the spatial
aspects of numerical data. The map focuses on the
variation of a numerical theme from place to place.
A quantitative thematic map can use two levels of data:
a.
Ordinal: Has order, but does not have equal distances. We,
at least, know that one thing we have measured is more or
less than another, but we do not know how much more or
less.
For example: A map displaying the distribution of earthquakes
categorized by high, medium, and low severity.
Summary
• Thematic maps can be either:
qualitative or quantitative.
• Data to display on a thematic map can be:
Nominal: distribution of a phenomenon without a
measurement. Label, category. (Qualitative)
Ordinal: Ranked data. High, medium, low or how
much greater than. (Quantitative)
Mapping data
There are many ways
to display qualitative
and quantitative
data.
To find your way on the local
bus system, you might use a
map showing bus routes.
By focusing on a specific topic,
or theme, maps like these
show information about some
aspect of physical or human
geography.
Some thematic maps focus on
physical geography. For
instance, they may display
Earth’s physical features, the
natural parts of Earth’s
surface.
Such features include
landforms like mountains,
valleys, and plains
Physical features also include
bodies of water such as
oceans, seas, rivers, and lakes
Thematic maps can also illustrate
other aspects of the physical
environment. For example, some
maps focus on climate, or longterm weather patterns.
Climate maps show how
much rainfall different
areas receive.
They also show how hot or
cold various places tend to
be in winter and summer.
Climate has a great effect on the
types of vegetation, or trees
and other plants, that will
grow in an area.
You can see this by comparing
a climate map of Earth with
a vegetation map.
A vegetation map shows the
kinds of trees and other
plants that grow in various
places.
Thematic maps can also focus on human
geography. Political maps of larger
areas show the borders between
countries.
Political maps also show
important cities, such as
the capitals of states and
countries.
Another type of thematic map
shows population density. This
is the average number of
people living in a unit of area,
such as a square mile.
Besides showing where people live,
a thematic map can show what
they do. A map of economic
activity focuses on the ways
people produce, buy, and sell
goods and services.
This kind of map might show the
main types of business and
industry in an area. It might also
show the natural resources that
fuel the area’s economy.
Natural resources are useful
items found in nature, such
as wood, coal, and oil.
• Choropleth,
Proportional/Graduated
Symbol, Digital Image,
Isoline/ and Dot
Distribution Maps
Choropleth Maps
• In these maps, each area
(spatial unit) is filled with a
color or pattern.
• These are the maps we
see most often.
Choropleth Map
•Maps that show the density
information about an area
“per unit area” are
choropleth maps. Also, a
map that would show who
owns what areas of land
would be a choropleth map.
Choropleth Map: Colorado
Counties
2000 Colorado Population Distribution
Map
Advantages of Choropleth Maps
•It provides an easy way to visualize how a
measurement varies across an area.
•Choropleth maps are also suitable for
indicating differences in land use, like the
amount of land or type of forest cover.
Disadvantages of Choropleth Maps
•It can be difficult to distinguish between different
shades in the maps.
Digital Images
•These maps are actually
digital images
•A grid of cells (pixels) are
assigned a color that
matchesto a specific value
or range of values
Digital Image Map
This kind of map is being
used to map environmental
occurrences seen from
remote sensing systems like
satellites
Population Density Map: 2000 World
Population Distribution
Digital Image Map: African
Population Density
Digital Image Map: Asian
Population Density
Digital Image Map: Population Density
North America
Proportional
Symbol/Graduated Symbol
Map
• In this type of a map, a
symbol is selected, usually
a circle because it’s easier
to work with.
Proportional Symbol Map
•The symbol will vary in its
size from place to place on
the map. This is because
the symbol represents
different quantities in
different places.
Advantages of proportional symbol
maps:
•They show data taking place 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:
•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
Disadvantages of isopleth maps:
They are not suited for showing
discontinuous distributions
•
• A large amount of data is required for
accurate drawing.
Dot Distribution Maps
• Dot distribution maps use
dots to show the quantity of
something in a given area or
areas.
Population distribution in US
Advantages of Dot Distribution Maps
• easy to understand
• show the varying density of a phenomena
Disadvantages of Dot Distribution Maps
•If dots get too dense, it is difficult to read