Topology editing is a special editing mode. After enabling it, the system will build a temporary topology based on all visible 2D line and polygon layers, allowing topological continuity between objects to be maintained during the editing process.

Before using topology editing, you need to first enable the editing state of the corresponding 2D line and polygon layers in the Layer Manager. Then, in the Topology editing drop-down menu in the Feature Editing group of the Edit Data tab, enable the Topology edit switches. Note that if there are no 2D line or polygon layers in editing state in the map, this function cannot be enabled.

Layers with read-only data sources or that are currently invisible cannot participate in topology editing. When the map is in dynamic projection state, topology editing cannot be used either. You need to turn off Dynamic Projection in the Map Properties panel before you can use it.

Topology editing mode provides the following dedicated tools: align edges, trimming, topology edit node. These three tools are only available after topology editing is enabled. In addition, after enabling topology editing, moving topology edges and topology nodes is supported while maintaining topological continuity; when topology editing is not enabled, it is in normal moving state and does not maintain topological continuity.

To help you better understand the topology editing function, the following provides a brief explanation of the related concepts involved in this function:

• Topology Node: A topology node is the intersection point of the geometries of all layers participating in topology editing in the map.
• Topology Edge: A topology edge is a continuous linear boundary, defined by two topology nodes.
• Topology Graph: A topology graph is composed of topology nodes and topology edges, used to represent the topology of objects in the map. When topology editing is enabled, the topology graph will be displayed on the layers within the current map extent.

  

This chapter will introduce the following contents:

• Move: Introduces how to move topology edges and topology nodes.
• Topology Edit Node: Introduces how to use the topology edit node tool to move, add, and delete object nodes.
• Trimming: Introduces how to use the trimming tool to trim topology edges.
• Align edges: Introduces trimming topology edges to match and coincide with another edge that shares two common topology nodes.