Advanced Editing: Rules-Based Topology in ArcEditor

What is Topology? Topology describes the spatial relationships between adjacent features, and uses x, y coordinates to identify the location of a particular point, line, or polygon. Using such data structures enforces planar relationships, and allows GIS specialists to discover relationships between data layers, to reduce artifacts from digitization, and to reduce the file size required for storing the topological data.

What is Topology? Historically, topology is the set of geometric relationships, determined mathematically, between connecting or adjacent features in a geographic dataset. e.g. FNODE#, TNODE#, LPOLY#, RPOLY# fields in a line (streets) ArcInfo coverage.

What is Topology? With advances in GIS software, topology has been taking on more of a rule-based approach. In a geodatabase, a topology is a set of governing rules applied to feature classes that explicitly defines the spatial relationships that must exist between feature data.

ArcView vs. ArcEditor Editing shared features is the same. ArcEditor – Topology or Map Topology ArcView – Map Topology ArcEditor – Rule-based (Topology) ArcView – Non rule-based (Map Topology)

Topology and Feature Geometry Geometries involved in a topology: Edges - Line segments that define lines or polygons Nodes - Points at the end of an edge

Topology and Feature Geometry Ways of sharing a geometry: Line features can share edges and nodes Vertices define the shape of edges Polygon features also share edges and nodes

Why Use Topology Ensure data quality Easily edit shared boundaries and features More accurately model the real world

Characteristics of a Topology Requires an ArcEditor or ArcInfo license. Can only be created for feature classes in a geodatabase. (not shapefiles) Feature classes participating in a topology must have the same spatial reference. A topology can only describe relationships between features within the same feature dataset of the same geodatabase. A feature class cannot participate in more than one topology.

Properties of a Topology Topologies store three sets of parameters: – Define the permissible spatial relationships between features. 1) Rules – The distance at which vertices are considered coincident. 2) Cluster Tolerance – Control which features may be moved to other features during validation. 3) Ranks

Properties of a Topology Topologies also maintain a feature layer that store: Areas that have been edited since validation. Requires another validation to discover any errors. Dirty Areas Errors Violations of a topology rule detected during validation. Exceptions Legitimate exceptions to a topology rule.

Topology Workflow Organize Data Setup the Topology Validate Entire Topology Check for Errors Done Errors Exist Fix Errors/Mark as Exceptions Validate Topology of Dirty Areas No Errors Edit Data

Building a Topology 1 Organize your data 2 Start the Topology Wizard

3 4 Building a Topology Name the new topology. Set the cluster tolerance. (in most cases, use the default value) 4

Building a Topology Determine which features you want to participate in the topology. 5

6 7 8 Building a Topology Set the number of allowed ranks. Set the rank of each feature class. 8 Begin adding rules to your topology.

Building a New Topology Rules used by DDP: Study Areas Must Not Overlap Study Areas Must Not Have Gaps Streets Must Not Self-Intersect Streets Must Not Self-Overlap Streets Must Not Have Dangles Streets Must Not Intersect or Touch Interior Schools Must be Properly Inside Study Areas.

10 9 Building a Topology The topology now appears in the geodatabase. Review the Summary Report & validate the topology.

Reviewing a Topology’s Properties Accessed through ArcCatalog or ArcMap

Time for Exercise 1 Follow the instructions in the handout. Stop at the end of Exercise 1.

Review the Topology Workflow Organize Data Setup the Topology Validate Entire Topology Check for Errors Done Errors Exist Fix Errors/Mark as Exceptions Validate Topology of Dirty Areas No Errors Edit Data

The Topology Toolbar Topology Drop Down Menu Show Shared Features Map Topology Button Validate Topology in Specified Area (AV Disabled) Construct Features Button Validate Topology in Current Extent (AV Disabled) Planarize Lines Button (AV Disabled) Validate Entire Topology (AV Disabled) Planarize lines: You can split selected lines that intersect each other @ their intersections. Topology Edit Tool Fix Topology Error Tool (AV Disabled) Error Inspector Button (AV Disabled)

Validating a Topology You have several options: Using ArcCatalog 2) Using ArcMap (during an Edit Session). c) Validate Entire Topology b) Validate in Current Extent a) Validate in Specified Area

Identifying Topology Errors Use either the Error Inspector or the Fix Topology Tool to find and identify topology errors. Error Inspector:

Identifying Topology Errors Fix Topology Tool: like a selection tool with more functionality

Fixing Topology Errors All topology fixes are done during an edit session in ArcMap. Select an error with the Error Inspector or Fix Topology Tool and apply one of the pre-described fixes. Different rules have different fixes available. Lets take a look…

Fixing Topology Errors in Study Areas Fixing Overlaps:

Fixing Topology Errors in Study Areas Fixing Gaps:

Fixing Topology Errors in Streets Intersect or Touch Interior, Dangles, Self-Intersections, Self-Overlaps Intersect or Touch Interior: Dangles: (Or select the features and click Planarize Lines )

Fixing Topology Errors in Streets Self-Overlaps & Self-Intersections:

Fixing Topology Errors in Schools Schools must be properly inside Study Areas:

Marking Errors as Exceptions In some cases you will have errors that break a topology rule, but are legitimate exceptions to that rule.

Time for Exercise 2 Follow the instructions in the handout Stop at the end of Exercise 2

Advanced Editing in ArcEditor Questions?

Other Topology Editing Moving shared features Using features in one feature class to construct features in other feature classes

Moving Shared Features

Constructing Features from Features in Different Feature Classes

Advanced Editing in ArcEditor Questions?