7.1 Geographic data: Vector boundaries & Area metadata

• Vector boundaries (polygons)
  • Data frame with one row for each ‘corner’ of a geographical region
    • lat and long: location of a point
    • group: a unique identifier for each contiguous region
    • id: the name of the region
    • Separate group and id are necessary because geo-graphical unit isn’t necessarily a polygon (e.g., islands of Hawaii)
  • Shape files contain vector boundary data (read them with e.g., readOGR())
  • geom_polygon(): Visualize the data (coordquickmap() for quick adjustment of aspect ratio)
• Area metadata
  • Sometimes metadata is associated with an area (rather than a point), e.g., census data on the county level
  • We’ll see an example further below