GEM 3390

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Lecture 31 Content

• Geographic Information Systems (GIS)
• Advanced GIS

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• Fuzzy sets
• Operations

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• What is fuzzy sets?
• GIS inception we assumed everything to be
  delineated using a distinct point, line and area
• Uncertainty was treated using statistical methods
• New approach in dealing with uncertainty,
  complexity, and vagueness in terms of fuzzy sets

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• Basic laws of thought by Aristotle
• The law of identity (everything is what it is ? a
  house is a house)
• The law of non-contradiction (something and its
  negation cannot both be true ? a house cannot be
  both a house and not a house), and
• The principle of excluded middle (every statement
  is true or false ? this house is lived in or it
  is not)

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• All statements in conventional logic can be
  either true or false (one or zero)
• Two-valued logic makes the following impossible
• Class overlap
• Partial membership of a set
• Partial truths

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• Not all geographical phenomena are clear-cut
• Much effort is on standardization of geodata
  (interoperability)
• Real life we make compromises ? if the phenomena
  is almost what we want we will gladly make do
• Unsure where the boundaries of the phenomena
  occurs between suitable and unsuitable
  classes
• Data collected are typically vague e.g. poorly
  drained, high dense, etc.
• Need for classification based on attributes that
  leads to unambiguous, non-overlapping classes
  with clear rules for allocation

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• Fuzzy
• Type of impression characterizing classes that
  for various reasons cannot have or do not have
  sharply defined boundaries
• Such classes are called fuzzy sets
• Used when there is ambiguity, vagueness
• The assessment of the possibility can be based on
  subjective, intuitive (expert) knowledge or
  preferences

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• Conventional sets which allow only binary
  memberships functions (true or false) are called
  crisp sets

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• Examples of fuzzy logic in GIS
• Where are areas of soil suitable for use as
  experimental fields?
• Which areas are under the effect of flooding?
• Which areas are polluted?
• Where on the ozone layer there is the likelihood
  that holes will form?

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• Fuzzy logic is slowly being introduced into the
  GIS environment
• Includes the use of expert and knowledge based
  systems (a form of artificial intelligence)
• Anticipated that this may lead to the use of
  virtual GIS

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• The End