Spatial Data Mining by Satoru Hozumi
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Spatial Data Mining by Satoru Hozumi

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Spatial Data Mining by Satoru Hozumi Spatial Data Mining by Satoru Hozumi Presentation Transcript

  • Spatial Data Mining Satoru Hozumi CS 157B
  • Learning Objectives
    • Understand the concept of Spatial Data Mining
    • Learn techniques on how to find spatial patterns
  • Examples of Spatial Patterns
    • 1855 Asiatic Cholera in London.
      • A water pump identified as the source.
    • Cancer cluster to investigate health hazards.
    • Crime hotspots for planning police patrol routes.
    • Affects of weather in the US caused by unusual warming of Pacific ocean (El Nino).
  • What is a Spatial Pattern?
    • What is not a pattern?
      • Random, haphazard, chance, stray, accidental, unexpected.
      • Without definite direction, trend, rule, method, design, aim, purpose.
    • What is a Pattern?
      • A frequent arrangement, configuration, composition, regularity.
      • A rule, law, method, design, description.
      • A major direction, trend, prediction.
  • Defining Spatial Data Mining
    • Search for spatial patterns.
    • Non-trivial search – as “automated” as possible.
      • Large search space of plausible hypothesis
      • Ex. Asiatic cholera : causes water, food, air, insects.
    • Interesting, useful, and unexpected spatial patterns.
      • Useful in certain application domain
        • Ex. Shutting off identified water pump => saved human lives.
      • May provide a new understanding of the world
        • Ex. Water pump – Cholera connection lead to the “germ” theory.
  • What is NOT Spatial Data Mining
    • Simple querying of Spatial Data
      • Finding neighbors of Canada given names and boundaries of all countries (Search space not large)
    • Uninteresting or obvious patterns
      • Heavy rainfall in Minneapolis is correlated with heavy rainfall in St. Paul (10 miles apart).
      • Common knowledge, nearby places have similar rainfall
    • Mining of non-spatial data
      • Diaper sales and beer sales are correlated in evenings
  • Families of Spatial Data Mining Patterns
    • Location Prediction:
      • Where will a phenomenon occur?
    • Spatial Interactions
      • Which subset of spatial phenomena interact?
    • Hot spot
      • Which locations are unusual or share commonalities?
  • Location Prediction
    • Where will a phenomenon occur?
    • Which spatial events are predictable?
    • How can a spatial event be predicted from other spatial events?
    • Examples
      • Where will an endangered bird nest?
      • Which areas are prone to fire given maps of vegitation and drought?
      • What should be recommended to a traveler in a given location?
  • Spatial Interactions
    • Which spatial events are related to each other?
    • Which spatial phenomena depend on other phenomenon?
    • Examples
      • Earth science:
        • climate and disturbance => {wild fires, hot, dry, lightning}
      • Epidemiology:
        • Disease type and enviornmental events => {West Nile disease, stagnant water source, dead birds, mosquitoes}
  • Hot spots
    • Is a phenomenon spatially clutered?
    • Which spatial entities are unusual or share common characteristics?
    • Examples
      • Crime hot spots to plan police patrols
  • Spatial Queries
    • Spatial Range Queries
      • Find all cities within 50 miles of Paris
      • Query has associated region (location, boundary)
      • Answer includes overlapping or contained data regions
    • Nearest-Neighbor Queries
      • Find the 10 cities nearest to Paris
      • Results must be ordered by proximity
    • Spatial Join Queries
      • Find all cities near a lake
      • Join condition involves regions and proximity.
  • Unique Properties of Spatial Patterns
    • Items in a traditional data are independent of each other, where as properties of location in a map are often “auto-correlated” (patterns exist)
    • Traditional data deals with simple domains, e.g. numbers and symbols where as spatial data types are complex
    • Items in traditional data describe discrete objects where as spatial data is continuous
  • Association Rules
    • Support = the number of time a rule shows up in a database
    • Confidence = Conditional probability of Y given X
    • Example
      • (Bedrock type = limestone), (soil depth < 50 ft) => (sink hole risk = high)
      • Support = 20 %, confidence = 0.8
      • Interpretation: Locations with limestone bedrock and low soil depth have high risk of sink hole formation.
  • Apriori Algorithm to mine association rules
    • Key challenge
      • Very large search space
    • Key assumption
      • Few associations are support above given threshold
      • Associations with low support are not interesting
    • Key insight
      • If an association item set has high support, then so do all its subsets
  • Association rules Example
  • Techniques for Association Mining
    • Classical method
      • Association rules given item types and transactions
      • Assumes spatial data can be decomposed into transactions
        • Such decomposition may alter spatial patterns
    • New spatial method
      • Spatial association rule
      • Spatial co-location
  • Associations, Spatial associations, co-location
  • Associations, Spatial associatins, co-location
  • Co-location Rules
    • For point data in space
    • Does not need transaction, works directly with continuous space
    • Use neighborhood definition and spatial joins
  • Co-location rules
  • Clustering
    • Process of discovering groups in large databases
      • Spatial view: rows in a database = points in a multi-dimentional space.
      • Visualization may reveal interesting groups
  • Clustering
    • Hierarchical
      • All points in one cluster
      • Split and merge till a stop criterion is reached
    • Partitional
      • Start with random central point
      • Assign points to nearest central point
      • Update the central points
      • Approach with statistical rigor
    • Density
      • Find clusters based on density of regions
  • Outliers
    • Observations inconsistent with rest of the dataset
    • Observations inconsistent with their neighborhoods
    • A local instability or discontinuity
  • Variogram Cloud
    • Create a variogram by plotting attribute difference, distance for each pair of points
    • Select points common to many outlying pairs
  • Moran Scatter Plot
    • Plot normalized attribute values, weighted average in the neighborhood for each location
    • Select points in upper left and lower right quadrant
  • Scatter plot
    • Plot normalized attribute values, weighted average in the neighborhood for each location
    • Fit a liner regression line
    • Select points which are unusually far from the regression line.
  • Conclusion
    • Patterns are opposite of random
    • Common spatial patterns:
      • Location prediction
      • Feature interaction
      • Hot spot
    • Spatial patterns may be discovered using:
      • Techniques like associations, clustering and outlier detection