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County Boundaries 
  • Managing data across time 
    • county boundaries and aggregations change yearly 
    • cross-time comparison requires comparable units 
    • boundary lines for all years in one Arc/Info coverage 
    • polygons coded with IDs for each year (1982, '85, '90, '96) 
    • aggregate to smallest common unit for comparing two years 
    • managed as Arc/Info Regions
 
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