SuperGIS Topology Analyst Extension > What is Topology Analyst?

What is Topology Analyst?

When digitizing a map, we need to input the coordinates of the surface on the paper map to the computer first; sequentially, convert the coordinates into a structure of point, line and polygon, so that the surface information in different types can be presented with such data structure(point, line and polygon). For instance, a point of a single coordinate is able to represent the location of a gas station; a line feature consisting of a series of coordinates is able to represent the expansion or distribution of a street; or a polygon feature composed by a closed area of a series of coordinates is able to represent a park.

To express what we mentioned above or to perform network analysis, we must make computers “understand” the “connectivity” of spatial relationships. That is, create Topology for spatial data. With Topology, the location of spatial data as well as the spatial connectivity relationships of features is able to be represented. For instance, which two nodes compose a line segment, which are the start point and end point of the line segment, how the line segments snap to others, which line segments compose a polygon feature, the adjacency relationships between polygons. Spatial data with topology avoids from repeatedly digitizing the common edge of two polygons and the common edge that is not coincident.

In network analyst, users must create topology first before analyzing and judging a road is one-way or two-way, overpass or underpass. Each vertex in the topological layer will be assigned an ID number, through the ID number and the attribute data we can get the desired road information. For instance, on a line segment of two nodes whose ID numbers are 1 and 2, if the attribute is 12, it means the road is a one-way road whose direction is from 1 to 2. If the attribute has both 12 and 21, it means the line is a two-way road. Two line segments that intersect, if their intersection is a vertex, it means the section is an intersection; if not, it means at least one of the two line segments is overpass or underpass. The topology is created based on the Rules in Topology Analyst; different rules are designed respectively for point, line and polygon. Please refer to Chapter 3 for details.