To Overlay Two Topologies

A powerful form of analysis is possible when you overlay two or more topologies.

To overlay two topologies

1. In Map Explorer, under Current Drawing, right-click the source topology AnalysisOverlay.
2. In the Topology Overlay Analysis - Analysis Type, do the following:
   • Select the type of overlay analysis to perform:
     • Intersect — Only areas that appear in both the source and overlay topologies are in the result topology.
     • Union — Areas that appear in either the source or the overlay topologies are in the result topology.
     • Identity — The result topology includes areas that appear in the source topology and areas in the overlay topology that are within the source topology boundary.
     • Erase — The result topology includes areas that appear in the source topology except where it is covered by the overlay topology.
     • Clip — The result topology includes areas that appear in the source topology except where they are outside the boundary of the overlay topology.
     • Paste — The overlay topology is "pasted" on the source topology.
   • Click Next.
3. In the Select Overlay Topology dialog box, do the following:
   • Select the polygon topology to use as the overlay topology.
   • Click Next.
4. In the Topology Overlay Analysis - New Topology dialog box, do the following:
   • Select Highlight to highlight the resulting topology onscreen. Select the highlight color.
   • Enter a name and description for the new topology, and specify the layer to place it on.
   • Click Next.
5. In the Topology Overlay Analysis - Output Attributes dialog box, do the following to copy data to the result topology:
   • For Source Attributes For New Topology, click (Expression Evaluator) to select the data from the source topology that you want to include in the resulting topology. You can include fields in an object data table or columns in an external database.
   • For Overlay Attributes For New Topology, click (Expression Evaluator) to select the data from the overlay topology that you want to include in the resulting topology.
   • Enter a name and description for the object data table that will store the data in the new topology.

     Object data and external database records are attached to the centroids of the result topology.

   • Click Next.
6. In the final dialog box, choose whether to create new nodes to complete the resulting topology. If so, specify which a block to use:
   • To use a point, leave the box blank or enter ACAD_POINT.
   • To select from a list of block definitions, click the down arrow.
   • To select a block saved as a DWG file, click Browse. Select the file to use.
7. For certain overlay operations, you also specify the block to use for centroids.
8. Click Finish.