Geographic Information Systems Data Analysis

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Geographic Information SystemsData Analysis
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What is GIS Data ?
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Types of GIS Systems

• Raster
• Features represented as a matrix of cells over
  continuous space
• Each layer is one attribute
• Analysis is done by combining layers to create
  new layers with new values
• Cell size is critical

• Vector
• Each feature is a row in a table
• Define by specific X,Y locations coordinates in
  space.(lat,long)
• Features can be discreet locations or events
  (trees or Earthquakes)
• Not as memory intensive

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Raster Data

• Grids represent entities
• Grids made of cells
• Value applied to cell
• Each grid represents one attribute
• Continuous surface of a matrix of cells

• Analysis IncludesAnalysis is done by combining
  layers to create a new layer with new cell values
• Buffering/Proximity
• Reclassification
• Hill-shade/Slope
• Interpolation
• Surface Calculation

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Varieties of geographic Data

• For a Vector System- 3 basic forms
• Map or location data -where is it?
• Attribute data- Information about it
• Image data- The real world

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Vector (Feature) Data

• Points, Lines and Areas represent entities

• Points - City, Tree
• Lines - River, Road
• Areas - Forest, Lake

• Analysis includes

• Buffering
• Intersecting
• Network Analysis (shortest path)

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Point Data
Points represent objects that have discrete
locations Usual to small to be represented by
area or polygon Can pinpoint the exact
location Eg. Buildings Spot heights Tornadoes W
ater samples Businesses
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Line Data

• Represent objects that have length but are too
  narrow to be shown as polygons
• Can be broken into many segments known as ARCs
• Eg.-rivers
• Roads
• Railways
• Bridges

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Area or Polygon Data

• Defined by borders and are closed
• Usually to large to be depicted as points or
  lines
• Can be legally defined building lots
• Administrative- countries or counties
• Naturally occurring boundaries- Ecozones
• Lakes

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Coordinate Systems

• A coordinate system is required to reference data
  to a real world location. It could be lat/long
  or military grid.
• ArcView transforms the image coordinates into
  real-world x,y coordinates.
• Vector data sources stored in a real-world x,y
  coordinate system.
• Images/Grids stored in rows and columns of
  pixels-
• Pixel size (resolution) is critical
• ArcView looks for georeferencing information
  stored with the image.

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Attribute data

• The descriptive data that a GIS links to map
  features
• Attribute data is collected and compiled to link
  to specific locational data-
• census data by Province
• often comes packaged with map data

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Image Data

• Data produced by an optical or electronic device.
  Usually originally in Raster format
• Remote sensed data
• Satellite remote sensed Data
• Aerial photography
• Scanned data
• Photographs
• Can be linked to locational data or registered to
  display with other themes and layers with real
  world coordinates

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What is GIS Analysis

• From simple to Complex
• Simple - Sometimes by just making a map you are
  doing analysis
• Complex - Sometimes we use many layers of data to
  simulate real world events

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Data Analysis

• What do we Map in a GIS?
• Map where things are-Location Analysis
• Map the most and least-Quantitative Analysis
• Map concentrations- Density
• Map what is inside-Monitoring
• Map what is nearby-Relationships
• Map Change-Prediction