Align Shared Vertices

Overview

The Align Shared Vertices tool standardizes the vertex coordinates of input features by a specified tolerance. The tool rounds X and Y coordinates to a tolerance grid and can optionally apply the same process to Z coordinates, making vertices with small coordinate differences become exactly identical coordinates.

This tool is suitable for small coordinate offsets caused by data conversion, floating-point errors, manual editing, or merging data from multiple sources. It can improve consistency along feature boundaries, nodes, and connections, but it is not a complete topology repair tool.

How It Works

The tool rounds each vertex to a grid. For the X coordinate:

$$x' = \operatorname{round}\left(\frac{x}{t_{xy}}\right) \times t_{xy}$$

Where $x$ is the original X coordinate, $t_{xy}$ is the XY coordinate tolerance, and $x'$ is the aligned X coordinate. The Y coordinate is processed in the same way. If Z coordinate tolerance is set, the Z coordinate is processed with the same type of formula.

After calculation, the tool keeps coordinates to 9 decimal places and filters out empty geometries. It supports point, line, polygon, and multipart geometries.

Use Cases

• Polygon features such as cadastral parcels, administrative areas, or planning boundaries have tiny gaps or boundary misalignments and need unified vertex coordinates.
• Line feature nodes such as roads, rivers, or pipelines have very small offsets that affect network connectivity or subsequent analysis.
• After multi-source data integration, boundary coordinates used in overlay analysis have floating-point differences.
• 3D line or polygon features need tolerance-based standardization for both XY and Z coordinates.

Parameters

Parameter	Description	Notes
Input vector file	The vector feature dataset whose vertices need to be aligned.	Required. Supports point, line, polygon, and multipart geometries.
XY coordinate tolerance	The tolerance used to round X and Y coordinates to a grid.	Required. Default: 0.001. The unit matches the coordinate system of the input features.
Z coordinate tolerance	The tolerance used to round Z coordinates to a grid.	Optional. If left empty, Z coordinates are not processed.
Output vector file	The aligned vector feature dataset.	Required. Input attributes are preserved.

Output

The output is a new vector feature dataset. Output attributes remain the same as the input attributes, and geometry vertex coordinates are standardized by the tolerance. Coordinates that originally fall on the same tolerance grid become exactly identical coordinates.

warning

This tool does not cluster nearby vertices and calculate average coordinates. Instead, it rounds coordinates to a tolerance grid. Therefore, two vertices that are close together but lie on opposite sides of a grid boundary may not align, while two vertices that should not move but fall into the same grid position may be standardized to the same coordinate.

Steps

1. Start the tool: Open Geoprocessing Toolbox > Vector > Feature processing > Build, then start the Align Shared Vertices tool pane.
2. Set the input: Select the Input vector file whose vertices need to be aligned.
3. Set the XY tolerance: Enter the XY coordinate tolerance based on data precision. In a projected coordinate system, the unit is usually meters. In a geographic coordinate system, the unit is degrees.
4. Set the Z tolerance: If the input contains 3D features and elevation differences need to be processed, enter the Z coordinate tolerance. Otherwise, leave it empty.
5. Configure the output: Set the path and name of the Output vector file.
6. Run and check the result: Click Run. After the tool finishes, check whether boundaries, nodes, and 3D heights meet expectations.

Notes

• A tolerance that is too large may noticeably change geometry shape. A tolerance that is too small may fail to remove existing small differences.
• If the input uses a geographic coordinate system, the XY tolerance unit is degrees. It is usually recommended to project the data to an appropriate planar coordinate system before processing.
• The tool standardizes all vertices, not only shared boundary vertices that are visible to the eye.
• After alignment, it is recommended to run Check Geometry to confirm that coordinate standardization has not created overly short segments, duplicate vertices, or invalid geometries.
• Before running the tool on production data, copy a sample area for trial processing and overlay it with the original features to check the displacement magnitude.