Documentation | Help File | UI | 2D Mode | Menu | Tools | Topology | Topology

Clicking on the Tools/Topology menu item invokes the Topology builder and corrector dialog box used to set up the topology correction task. The Topology builder and corrector feature are capable of analyzing and correcting the topological properties of both the line and polygon type layers. As a result, a topology project is created consisting of the corrected layer and, optionally, report layers each representing the result of a different stage of the topology analysis. The Topology builder and corrector feature are capable of detecting the following types of topology elements and errors:

Name	Example (red)	Description
centroid		Center point of a polygon; a centroid is always forced to lay within its polygon.
intersection		A point where two segments of some polygons outlines cross.
correct polygon		A polygon that has no topology errors.
overlap		A polygon covering the area, where at least two polygons overlap.
hole		A polygon covering the area, where at least two touching polygons outlines branch off and touch again afterwards; also, a polygon internal hole
edge		A polygon outline that is topologically correct.
dangling edge		An element of the polygon outline that gives no contribution to the polygon area.
external border		If all the polygons in a layer are touching forming one “island”, the outline of that “island”; otherwise, the outline of the leftmost “island”

To build a topology project for a vector layer

1. Activate (highlight) the vector layer that is to be analyzed. Do this by clicking on its name in the Legend.
2. Click on the Tools/Topology menu item - this invokes the Topology builder and corrector dialog box.
3. Within the Topology builder and corrector dialog box set the name and path of the topology project file. First, click on the […] button in the Output project file field- this invokes the Save As dialog box.
4. Within the Save As dialog box go to the drive on which you want to store the project file.
5. Enter the folder in which you want to save the project file.
6. Enter a name for the project file in the File name field.
7. Click on the Save button - this brings back the Topology builder and corrector dialog box.
8. The Topology builder and corrector feature can analyze only one type of shapes at a time. If the layer to be analyzed contains more than one type of shapes, e.g. lines and polygons, then select the appropriate shape type in the Input type.
9. Choose the type of topology to be analyzed in the Topology type box.
10. In the Additional layers list choose which additional layers should be added to the topology project - see Additional layers below.
11. If the Input type feature is set to Lines and the Topology type is set to Linear, the Linear topology options become available and can be used. For detailed information see Linear topology options below.
12. In the Tolerance (layer units) field set the tolerance used for topology correction; if zero, the topology correction is not performed.
13. Click on the OK button - the Progress… message box will appear informing about the progress of the topology analysis.
14. When the process of topology analysis completes without encountering any error a message box will appear informing about the success - confirm it by clicking on the OK button.
15. Another message box will appear asking if the user would like to open the newly created topology project - click on the OK button to open the result of the topology analysis.

Topology builder and corrector dialog box.

• intersection field - if checked, a crossing of segments of two lines will be regarded as an intersection only if those lines have a different value of the attribute selected from the list,
• merging field - if checked, if a dangling node of a line has the same coordinates (up to the Tolerance) as a dangling node of a different line, then those two lines will be merged to form a single shape only if they have the same value of the attribute selected from the list,
• edges merging - if checked, if a dangling node of a line has the same coordinates (up to the Tolerance) as a dangling node of a different line, then those two lines will be merged to form a single shape.

The following additional layers can be added to the topology project:

• intersections - point type layer indicating coordinates in which two lines or polygon outlines intersect,
• nodes - point type layer indicating coordinates of all vertices belonging to a line or a polygon outline,
• edges - line type layer containing all lines and polygon outlines,
• centroids - point type layer containing centroids of all polygons.

• The topology project layers are generated to the ArcView Shape File (SHP) format. The attributes are stored in the Data Base File (DBF) type files.
• The correction tolerance is defined in layer units. If the layer has a coordinate system set, the layer units are assumed to be the units of the coordinate system. Therefore it is necessary to know the coordinate system of the corrected layer in order to set a reasonable tolerance.
• Note, that some of the coordinate systems are defined in angular units. However, defining the tolerance in angular units is not recommended because it is different in points of different latitude.