Aligning features in ArcGIS 10.1: Aligning features by tracing

Note: You can view this post as a video: Aligning features by tracing.

In my previous post, I used some of the new alignment tools to match edges. Just slightly west of the location I was editing before, I noticed a stream line that should be coincident with the borders of the land-use polygons. Although there are several ways I could adjust the stream, I am going to use the new Align To Shape tool because it allows me precise control when updating shapes. Unlike the other tools I have been using, Align To Shape is located on the Advanced Editing toolbar and does not require a topology.

Align To Shape adjusts all features in the layers I specify to match a shape that I trace. Align To Shape is commonly used to align features that have been captured at different resolutions, scales, or time periods, which cause edges to become braided, overlap, or have gaps between them. In this case, the streams were created at coarser resolution than the land-use polygons.

When I click Align To Shape, a dialog box opens so I can set the adjustment parameters. I first create the shape to align to by tracing the edges of existing adjacent features. Since I want to align the stream layer to the edges of the land-use polygons, there are a few tricks I can use to make sure I trace the correct alignment path. Because the Align To Shape dialog box allows me to interact with the map while it’s open, turning off the Streams layer and displaying only the Land uses layer helps avoid tracing along the stream line. I can also select the polygons and press the CTRL key to limit the alignment shape trace to the edges of selected features only. The ESC key allows me to restart tracing if I make a mistake and need to redraw the alignment shape.

Once I have the alignment shape traced, I choose to adjust the Streams layer and set the alignment tolerance. Any portions of features in the Streams layer that are within the tolerance are aligned to the path I traced. For a layer to be listed, it must be a point, line, or polygon layer that is editable and visible (turned on and not hidden at the current scale because of a visible scale range). The map shows a transparent buffer to represent the current alignment tolerance value, which is given in the data frame coordinate system’s map units. Since the map preview is updated as I change the tolerance, I can immediately see if the alignment appears as I want it. It may take a few attempts to find a tolerance value that aligns features correctly, since initially some of the edges may be outside the tolerance.

Once I am satisfied with the preview, I click Align to perform the adjustment. Now, the stream is coincident with the land-use polygons. Because Align To Shape is an interactive tool that requires manually tracing the shape to align to, it works best for cases such as this one where just portions of features need to be adjusted.

Because I still have the map topology built on these layers, I can select the edges and check that they are coincident using the Shared Features window.

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  1. dsettahr says:

    Is there any way to select the edge to align to other than by tracing? I have a large, complex, multi-part feature than I need to align other features to, and using this method, while it produces excellent results, would take forever if I were to trace the outlines of every polygon.

    If there is currently no way to do this, are there plans to add other ways to select edges to align to in future versions of ArcGIS? Ideally, in addition to tracing, there would be an option to select all the edges of a particular feature, and an option to select all the edges of selected parts of a feature.

    • Rhonda Glennon says:

      Align To Shape was designed to be used only on portions of features. (It’s somewhat similar to the old Zipper tool developer sample, for those familiar with it). This help topic describes the current set of alignment tools and when you might use them:

      For whole features or entire layers, geoprocessing tools are the best option. However, it sounds like from this forum thread, you’ve already tried them. With a really complex feature, like coastlines with lots of small, disjoint multipart polygons, geoprocessing tools may provide results, but often the small parts get dropped or merged, which may not be ideal for you.

      You can contact Esri support to see if an analyst can help with your scenario, particularly to see if geoprocessing tools would work, or submit an enhancement request through ArcGIS Ideas.

      • dsettahr says:

        Thanks. Looking through the set of alignment tools I see something that I hadn’t found before- Spatial Adjustment. It sounds promising. I’ll give it a try and see if it works.

        If nothing else works, the snap model I mentioned in the thread will work for me. I’ll be sure to make a post on ArcGIS ideas. It’d be nice to see some improved functionality for the Align to Shape tool.

  2. td_allpoints says:

    Hi Rhonda,
    I’m wondering if you can help me out. The align tool seems to work great but I’d like to control which features the trace tool will snap to. Can you set the trace tool to only snap to 1 feature so I can only trace 1 feature? It seems to jump around to different features that are close together or intertwined? And I have to zoom in to make sure that I only follow the feature that I want to trace.
    Thanks – Tom