TIGER/LINE(TM) Files, 1992
 
                           Appendix B
              SDTS Definitions for Spatial Objects
 
 The spatial objects in TIGER/Line belong to the "Geometry 
 and Topology" (GT) class of objects in SDTS.  The 
 definitions are from FIPS Publication 173, SPATIAL DATA 
 TRANSFER STANDARD (SDTS) (August 28, 1992) Section 2-2, 
 Classification and Intended Use of Objects,  pp. 11-20.
 
   *  Node:  "A zero-dimensional object that is a 
      topological junction of two or more links or chains, or 
      an end point of a link or chain," is a node.
 
   *  Entity point:  "A point used for identifying the 
      location of point features (or areal features collapsed 
      to a point), such as towers, buoys, buildings, places, 
      etc."
 
   *  Complete chain:  "A chain [a sequence of non-
      intersecting line segments] that explicitly references 
      left and right polygons and start and end nodes."  The 
      shape points combine with the nodes to form the segments 
      that make a complete chain.
 
   *  Network chains:  "A chain that explicitly references 
      start and end nodes and not left and right polygons."
 
   *  GT-polygon:  "An area that is an atomic two-
      dimensional component of a two-dimensional manifold, 
      [which is defined as] one and only one planar graph and 
      its two-dimensional objects."  GT-polygons are 
      elementary polygons that are mutually exclusive and 
      completely exhaust the surface.