Exercise 1: Interactive vectorization

Complexity: Beginner Data Requirement: ArcGIS Tutorial Data Setup

ArcScan makes it easy to create new features from scanned raster images. This process can significantly reduce the time it takes you to incorporate raster data into your vector database.

In this exercise, you will generate features from a scanned parcel map by interactively tracing raster cells. You will begin by starting ArcMap and loading a map document that contains the raster dataset and two layers.

Setting up the ArcScan environment


You need to have the ArcScan for ArcGIS extension installed and registered. In addition, start ArcMap and add the Editor and ArcScan toolbars to the display.

  1. Click the Open button Open on the Standard toolbar.
  2. Navigate to the ArcScanTrace.mxd map document in the ArcScan directory where you installed the tutorial data and select it (C:\ArcGIS\ArcTutor is the default location).
  3. Click Open.
  4. To use ArcScan, you need to enable the extension. Click the Customize menu, click Extensions, check ArcScan, then click Close.
  5. Raster layers must be symbolized as two-color images to use the ArcScan tools and commands. You will change the raster symbology from stretched to unique values. Right-click the ParcelScan.img raster layer in the ArcMap table of contents and click Properties. The Layer Properties dialog box appears.
  6. Click the Symbology tab on the Layer Properties dialog box.
  7. Click Unique Values in the Show box.
    Turning on the Unique Values renderer
  8. Click OK.

Setting the raster snapping environment

ArcScan is designed to work in conjunction with the ArcMap editing environment and is only active when an edit session has been started. You need to set some options for snapping while editing and using ArcScan.

  1. Click the Editor menu and click Options.
  2. ArcScan uses the classic editing snapping environment rather than the Snapping toolbar.
  3. Click the General tab.
  4. Check Use classic snapping.
  5. When you enable classic snapping, it disables the Snapping toolbar's snapping environment for use in editing. Therefore, once you have completed your work with ArcScan, you should reenable the Snapping toolbar by unchecking the Use classic snapping box.
    Enabling editing classic snapping
  6. Click OK.
  7. The ArcScan extension is only active in an edit session. The Start Editing command allows you to begin an edit session.
  8. Click the Editor menu on the Editor toolbar and click Start Editing.
  9. Choose to start editing on the file geodatabase workspace and click OK.
  10. Raster snapping requires settings that influence the behavior of the tracing. These options are set on the Raster Snapping Options dialog box.
  11. Click the Raster Snapping Options button Edit Raster Snapping Options on the ArcScan toolbar to open the Raster Snapping dialog box.
  12. Set the maximum line width value to 7. This setting will ensure that you are able to snap to raster cells that represent the lot boundaries.
    Setting the options for raster snapping, including the maximum line width
  13. Click OK.
  14. Click the Editor menu, point to Snapping, then click Snapping Window.
  15. Click the plus sign next to Raster to expand it.
  16. Check the Centerlines and Intersection options for raster snapping. You can close the window when you are done.
    Turning on raster snapping
  17. Now, you need to turn on SnapTips, which are pop-up messages that give you information on the type of snapping that is active as you move your pointer around the map.
  18. Click the Editor menu, point to Snapping, then click Options.
  19. Check Show SnapTips.
  20. Click OK.

Creating line features by tracing raster cells

Now that you have set up your raster snapping environment, you are ready to begin tracing the raster cells. You will use the Vectorization Trace tool for this step.

  1. Click Bookmarks and click Trace lines to set the current view to the edit area of the exercise. When the display refreshes, you should see the trace area.
    Section of the raster image to be traced
  2. Click the ParcelLines line feature template in the Create Features window. This sets up the editing environment to create new features in that layer using the default attributes for that template.
    Choosing the ParcelLines feature template
  3. Click Vectorization Trace tool Vectorization Trace on the ArcScan toolbar.
  4. Move the pointer until it snaps to the intersection of the lot boundaries and click to start tracing.
    Snapping to a raster intersection
  5. Point the Vectorization Trace tool downward and click to start creating the line feature.
    Starting to trace
  6. Continue to point and click with the Vectorization Trace tool to trace the exterior boundary of the lots.
    Tracing around the feature
  7. Once you have finished tracing around the lot boundaries, press F2 to finish the sketch.
    Sketching around the entire feature

    A line feature now represents the exterior boundaries of the scanned parcel lots.

    New lot line feature

Creating polygon features by tracing raster cells

Now that you have successfully traced raster cells to create line features, you will create polygon features using the Vectorization Trace tool.

  1. Zoom to the bookmarked extent called Trace polygons to get a better view of the area that will be traced. Click Bookmarks and click Trace polygons.
  2. Click the ParcelPolygons polygon feature template in the Create Features window. You must change the active feature template to ParcelPolygons to create polygon features while tracing.
  3. Click the Vectorization Trace tool Vectorization Trace on the ArcScan toolbar.
  4. Move the pointer until it snaps to the lower-left corner of lot 061 and click to start tracing.
    Starting to trace the new polygon feature
  5. Point the arrow toward the lower-right corner of the lot and click to start creating the segments of the polygon feature.
    Tracing around the polygon
  6. Continue to trace the lot boundary in a counterclockwise direction.
    Sketching around the entire feature
  7. When the cursor has returned to the starting point of the trace, press F2 to complete the polygon.
    New polygon feature
  8. Once you have finished tracing the raster cells, you can stop editing and complete the exercise by saving your edits.
  9. Click the Editor menu on the Editor toolbar and click Stop Editing.
  10. Click Yes to save your edits.
  11. To continue to the next exercise in the ArcScan tutorial, click Exercise 2: Automatic vectorization.

In this exercise you learned how to set the raster snapping options and environment, snap to raster cells, and trace raster cells to create new line and polygon features. These steps covered the main components of the raster tracing process. The next exercise will show you how to edit a raster layer and automatically generate features for an entire raster layer using the batch vectorization tools.

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Published 6/8/2010