Survey Extent Polygon

The Survey Extent Tool creates an initial polygon that is used to constrain the interpolation of the TIN (i.e. boundary of the survey area). It essentially automates the running of the built-in ArcGIS Aggregate Points geoprocessing tool.

The Survey Extent polygon must be inspected for errors in how it delineates the edge of the data. If the polygon is not ideal, then users may either re-run the Survey Extent Tool using a different edge tolerance or edit the polygon manually.


  1. Make sure teh survey data are projected (imported as projected or been run through the Coordinate Transformation Tool).
  2. Open Create Survey Extent Polygon from the Workflow Manager.
  3. Make sure the correct topo project is open.
  4. Hull Tolerance: The general distance between points along the boundary of the survey. In general, use larger values for larger area surveys with greater point spacing along the margins (15m to 20m or more) and smaller values for smaller area surveys or surveys with higher point density (10m to 15m). Note: this is the original tolerance parameter of the Survey Extent Tool from previous versions of the Toolbar.

  5. Snap Tolerance: After the initial polygon is generated using the “hull tolerance”, any edge within this distance of any survey point will be snapped to those points. This is useful for cleaning up edges along the in channel areas at the top and bottom of the survey. Typically a value of 1m is appropriate, though larger surveys with lower point density could use a higher value.

  6. Click OK to run the Tool.

  7. The Survey Extent Polygon will be added to the map. Check the following:

    • Longitudinal boundaries (out of channel) generally follow the stream channel and all areas that were adequately surveyed are included in the bounding area. Make sure there are no “jagged” edges.
    • End of reach transects (in channel) are surveyed with a higher density of points than locations along the out of channel margins. The Snap Tolerance should capture these areas fairly well, but should still be inspected for accuracy.
  8. If the survey extent polygon does not look good, you may re-run the Survey Extent Tool with a different tolerance value. 1.If the Survey Extent polygon looks good overall, but has only a few errors, you may manually edit the polygon.

    • Right click on the Survey Extent Layer in the Table of Contents and select “Edit Features\Start Editing”.
    • Use the Edit Tool to select the Survey Extent Polygon for editing.
    • Use the Edit Vertices Toolbar to edit the Survey Extent Polygon.
      • Move or delete vertices if the boundary is too small or detailed (excludes areas for interpolation)
      • Add Vertexes to add detail/definition to the boundary. This is a common task for the End of Reach transects across the channel.
    • Stop the Editing Session and make sure to save edits when you are done.

After you have generated and checked the Survey Extent Polygon, you may proceed to generating a Topographic TIN.


  • Make sure the Editor is turned off when running the tool.
  • Feature classes must be Projected and located in the Projected Feature Dataset within the Survey Geodatabase.
  • This tool only works with ArcGIS version 10.1.

If the tool continually fails to run successfully, it may be necessary to create the Survey Extent polygon manually.

  1. Close ArcMap (save the map document).
  2. Open ArcCatalog and navigate to the SurveyData folder in the topo project folder in the Catalog Window.
  3. Right click on the Projected Feature Dataset (in the Survey Geodatabase) and select “New\Feature Class”.
  4. Use the wizard to create a new Polygon Feature Class:

    • Name: Survey_Extent
    • Alias: Survey Extent
    • Type: Polygon Features
    • Leave all other options set to their default value. Click Next until you get to the end of the wizard, then click Finish.
  5. Close ArcCatalog and re-open the ArcMap Document you closed in step 1.

  6. Add the Survey Extent feature class to the Map Document.

  7. Right click on the Survey Extent Layer in the Table of Contents and select “Edit Features\Start Editing”.

  8. In the Create Features Panel, select the “Survey Extent” template and the “Polygons” Construction Tool.

  9. Digitze the Survey Extent Polygon by hand, making sure to snap all of the polygon vertices to Points or breakline vertices.

  10. Stop the Editing Session and make sure to save edits.