ArcGIS provides several tools to help you align your data. Depending on your workflow, one tool may be more appropriate than others.
Scenarios that result in data alignment issues
When editing, you commonly compile data from various sources with different levels of quality assurance. Unfortunately, this can often result in data alignment problems and topological errors. These are some of the most common causes:
- Editing methods that help ensure spatial integrity, such as snapping or geodatabase topology, were not utilized when the features were created.
- Different data compilation techniques or data sources were used to capture portions of the dataset. This is often the case when other software packages or contractors compile and maintain the dataset.
- Features were created or updated at different points in time. In many cases, newer data is more accurate, since current imagery or higher-resolution capture techniques are more likely to be available.
- Features were created at different map scales, resulting in various levels of detail and capture accuracy.
Types of tools available in ArcGIS
ArcGIS provides a set of tools on the Advanced Editing, Topology, and Spatial Adjustment toolbars to help you align your data, in addition to several geoprocessing tools. You can use them to align portions of features, several features at a time, or entire datasets through manual or bulk and semiautomated manners. The following table describes some of the available tools, their functionality, and the scenarios in which they are most useful or cases in which they are less efficient or limited.
|Tool||What it does||Scenarios where the tool works best||Limitations|
Align Edge (Topology toolbar)
Align Edge provides a quick way of matching one edge to another edge by using topology.
Align Edge works best for fixing gaps between polygons and making long edges match among features.
Align Edge is less useful when attempting to fix edges that are braided, where some edges overlap and some edges have gaps. Edges such as these are better fixed with Align To Shape.
You can fix overlaps with Align Edge, but they may be harder to see because underlying edges are hidden by the features drawn on top of them.
Align To Shape (Advanced Editing toolbar)
Align To Shape adjusts features in certain layers to a line you trace along an existing feature.
Align To Shape works well to update multiple layers when you want some control over the parameters used in the alignment. This includes the shape to align to, which layers are updated, and the tolerance.
Since Align To Shape is an interactive tool that requires that you manually trace the shape to align to, it works best for cases where just portions of features need to be adjusted, rather than when you have many features to align.
The tools in the Editing geoprocessing toolbox perform global changes to data, such as snapping, extending, and trimming.
The tools are best used after importing features into a geodatabase, such as from a CAD file. They are also helpful to clean up datasets that have many topological issues.
The geoprocessing tools work in an automated manner, so should not be used if you need fine-control over the resulting alignment.
In addition, once your data is topologically sound, use caution performing bulk changes. For example, the Generalize geoprocessing tool can cause gaps or overlaps to appear between polygons that were formerly coincident. In this case, use Generalize Edge instead because it uses topology, which considers shared edges and adjusts all coincident features at once.
Generalize Edge (Topology toolbar)
Generalize Edge simplifies the shapes of features that share one or more topology edges.
Common use cases for Generalize Edge include to minimize vertex count, eliminate true curves, or standardize dataset to a given level of detail.
You can use Generalize Edge to update multiple edges at once, and all the features that share those edges.
Geodatabase topology allows you to find and identify violations of specific topology rules and apply standard fixes to remove the errors.
Geodatabase, topology often allows you to find and fix multiple spatial integrity errors at the same time in one edit. For example, when aligning polygon data, you typically want to apply the Must Not Have Gaps and the Must Not Overlap topology rules to ensure the polygons form a continuous fabric. You can also maintain coincidence among point, line, and polygon layers.
Geodatabase topology is also helpful to supplement the other alignment tools. You can maintain geodatabase topology rules on your data and periodically validate the topology to confirm that your edits have not introduced errors.
Geodatabase topology requires an ArcGIS for Desktop Standard or ArcGIS for Desktop Advanced license. It is also only available for data in a geodatabase and cannot be used on shapefiles.
Replace Geometry (Advanced Editing toolbar)
Replace Geometry completely updates the shape of a feature with a new geometry you sketch, while maintaining the original attributes.
Replace Geometry is useful in cases where it is easier to start over with the shape of a feature than to attempt to reshape large portions of it. You can trace the previous shape or another feature's shape.
Replace Geometry works on one feature at a time, so can be time-consuming if you have many features to update.
Reshape Edge (Topology toolbar)
Reshape Edge allows you to reshape all the features that share one or more topology edges.
Reshape Edge is useful when you need to update the portion of the feature shape, such as modifying boundaries to match an aerial photograph.
Spatial adjustment methods (Spatial Adjustment toolbar)
Spatial adjustment aligns features using links that set control points between the features being aligned and the control features.
Spatial adjustment works well for adjusting an entire layer or many features over a wide area.
Spatial adjustment is less useful for aligning data in a localized area. You can use other alignment tools more efficiently in those cases.