GIS to get information..

• GPS system


  Antennas receive signals from satellites above, calculates position by measuring time it takes for signal to travel from satellite to receiver
• How GPS calculates position

  1. Knows where each satellite is from almanac

  2. Measures time it takes for signal to travel from satellite to receiver

  3. Triangulates position using signals from at least 4 satellites
• GPS system


  • Wider distribution of satellites in the sky improves accuracy
  • Signals from satellites over the horizon are not used due to inaccuracy
  • Uses signals from American, Russian, and European satellite systems
• Interferometry


  Comparing the wavelengths of radio waves from satellites to determine exact position within a wavelength
• GPS accuracy


  • Can achieve centimeter-level accuracy by comparing errors between base station and rover
  • Biggest errors come from moisture in atmosphere and ionosphere affecting signal path
• Types of operations in GIS

  • Local
  • Neighborhood
  • Global
• Local operation


  1. Concerned with the values associated with one polygon

  2. Example: looking at population density for one state (Utah)
• Neighborhood operation


  1. Concerned with the values associated with adjacent polygons

  2. Example: looking at population density for Utah and its 6 adjacent states
• Global operation


  1. Concerned with the values associated with all polygons in the dataset

  2. Example: ranking western US states by total population
• For neighborhood operations, we have to consider the location or values of associated polygons in addition to the polygons we're interested in
• For global operations, we're looking at the entire dataset, not just a globe