GIS for K-12 Education

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Thematic Mapping Data Classification
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Thematic Mapping Data Classification

• What is a thematic map
• Qualitative vs. Quantitative
• Data types
• How do we map this data?
• Considerations

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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.

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Types of Thematic Maps

• Thematic maps can be divided into two groups
• 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

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Types of Thematic Maps

• 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
• 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.

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Quantitative Thematic Map

• A quantitative thematic map can use two levels of
  data
• b. Interval/Ratio This is the very best type of
  data. Ratio/Interval data has the most precision,
  and can measure things in greater detail. It
  contains numbers, therefore contains a wealth of
  information.
• For example A map displaying the distribution
  of the magnitude of earthquakes.

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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)
• Ratio/Interval how much different, measured by
  numbers. (Quantitative)

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Mapping data

• There are many ways to display qualitative and
  quantitative data.

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Choropleth Maps

• Many quantitative thematic maps are called
  choropleth maps. It has also been called shaded
  or area mapping.
• This is a a thematic mapping technique that
  displays a quantitative attribute using
  ordinal/ratio/interval classes applied as uniform
  symbolism over a whole spatial feature. The
  boundaries of the spatial areas are determined by
  the user.
• Example A map displaying population across
  Canada. This could be mapped using province
  boundaries or census boundaries depending on the
  level of data you have.

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The problem with this is.how does the GIS
determine where the breaks in data are? This is
called data classification. It is ultimately up
to the cartographer to determine which
classification method best illustrates what the
intention of the map is.
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Data Classification

• In order to learn more about data classification,
  please click on the link below for a PowerPoint
  on
• Data Classification!