GIS12

Topology
GIS features are represented as Points [Nodes], Lines [Arcs] and Polygons [Regions]
For generating “NEW” information, we must know more about the linkages that these objects have in relation to each other
By Interpreting Spatial Relationships, Identify “CONNECTING” lines along a path, defining areas or “POLYGONS” enclosed by groups of lines, and by identifying “CONTIGUOUS” areas.
Topology is that branch of mathematics which concerns itself with the concepts of :
DIRECTION  , CONNECTIVITY  , ADJACENCY or CONTIGUITY and  PROXIMITY
Topology Defined
Mathematically explicit rules defining “linkages” or “relationships” between spatial elements/objects ,Relationships include:
     directions, relative locations, containments, contiguities
TOPOLOGICAL DATA STRUCTURES
Vector Data Structures that incorporate explicit spatial information about the relative locations of objects in the data tables Required for flow, proximity models and for advanced analysis within the vector GIS context
Topology --Terminology and Uses
Topological data structures are founded upon two types of objects and their generic relationship:
Objects are “NODES” or “EDGES”, the basic relationship between them being “INCIDENCE”
Topological data structures store and manipulate logical relationships between map features
Topological data structures are used to “BUILD” point, line or polygon feature classes, based on node and arc-node topology
Topology in Action
Direction   from and to nodes [Line L1 from Node N1 to Node N2], line L1 therefore has right and left sides
Connectivity  Polygon Enclosure [Lines L1, L2, L3 and L4 “enclose” the Right Polygon
Adjacency  polygon “line-sharing” [Line L1 common to both polygons]
Proximity   node X-Y locations