Organization of data
--------------------
Tiger Database (full nation)
      |
   Dataset (directory containing info for a single county)
      |  - how these are organized in filesystem is critical
      |  - do summaries for these exist?
    Layer (data covering a specific theme -- basename)
      |  - summarized in LYR file
   Object (coordinates and other info for each object)
         - summarized in SUM file


Overall layout of tigerwww drawing routines
-------------------------------------------
DrawMap     (draw entire map on image )
  | DrawGraticule
  | DrawDatasets    (draw all visible data)
  |   |for each candidate dataset: (i.e. directory for a county)
  |   |  is the scale level correct (detailed or generalized)?
  |   |  is the dataset visible?
  |   |  if so, DrawLayers (draw all layers in that directory)
  |   |    |for each layer file: (i.e. a theme)
  |   |    |  is the theme one of those requested?
  |   |    |      (I'm not sure if this info is in the LYR file)
  |   |    |  if the layer visible?
  |   |    |  if so, DrawObjects
  |   |    |    |for each record in SUM file: (i.e. an object)
  |   |    |    |  is the object visible?
  |   |    |    |  if, so DrawObject
  |   |    |    |    |read in basic info from OBJ file
  |   |    |    |    |is the feature type (CFCC) requested?
  |   |    |    |    |if so, read and draw coordinates
  | Write GIF image to file