Note: You can view this post as a video: Creating a map topology.
Aligning features and editing coincident geometry is easier with ArcGIS 10.1. In a series of posts, I will be highlighting some of the new tools available to update features that share geometry. I am working with a set of layers representing land uses, hydrologic features, and administrative boundaries near Mammoth Cave National Park in Kentucky. I need to align some of the features to make them coincident and be able to edit several features simultaneously. The alignment tools in ArcGIS 10.1 make it simpler and quicker for me to perform these updates on my data.
I am first going to use the topology editing tools to update the features that currently share boundaries because topology allows me to update multiple features at once and ensure they stay coincident. As in previous releases, there are two kinds of topology in ArcGIS: map topology and geodatabase topology. Creating a map topology is quick and allows me to edit features that are coincident, which is all I need for my Mammoth Cave edits. A geodatabase topology requires more effort to set up and modify, since it provides rules that define complex relationships about how the features share geometry. Once the topology is set up, the editing tasks are similar regardless of whether a map topology or geodatabase topology is being used.
Setting up a map topology
After I start editing, I display the Topology toolbar, which has been redesigned in ArcGIS 10.1 so it only contains commands that are directly related to topology. The commands that were previously on this toolbar but do not require a topology, such as Construct Polygons, have been moved to the Advanced Editing toolbar.
To begin working with topology, I click the Select Topology button (the first button on the left end of the toolbar), which integrates into a single dialog box the experience of creating a map topology and using the Topology toolbar drop-down list to set the active topology. Since I do not have a geodatabase topology in this map, I am going to use the Select Topology dialog box to create a map topology by specifying the layers that should be edited together. In my case, I only need to edit the Streams and Land uses, so I check those layers to participate in the map topology. In ArcGIS 10.1, map topology uses layer information and reflects layer properties, including name and visibility, rather than the properties of the underlying feature class.
I can click Options to view the cluster tolerance, which is the distance that defines how close together edges and vertices must be to be considered coincident. Since ArcMap automatically determines the minimum possible cluster tolerance, I am using the default because increasing the value can cause features to collapse or distort.
That’s all I need to do to set up my map to edit coincident features. If I happened to click a topology editing tool without having an active topology, I would be prompted to create a map topology using this dialog box. Once I have an active topology, I can take advantage of some of the topology improvements, including selecting, reshaping, and generalizing edges.