Digitizers can go overboard trying to accurately represent feature shapes. Accuracy is important, but for some maps you don’t need a lot of feature detail. For example, when creating a map that will be published to the Web, it is recommended to use generalized data when possible to optimize performance (draw speed).
The number of vertices in a feature indicates the level of detail it represents (the more vertices, the greater detail). If you have a dataset in which most of the features are simple shapes with few vertices but some are quite detailed, you can use the ArcMap Generalize editing tool to reduce the number of vertices in the more detailed features. Here’s how:
- Start ArcMap, open a new map document, and add the dataset you want to edit.
- Display the Editor toolbar, start an edit session, then zoom into a feature you want to generalize.
- Using the Edit tool, double-click the feature to display its sketch and update the edit task to Modify Feature.
We’ll use the parcel shown in the graphic below as an example of how to complete the remaining steps. Notice that many vertices (green boxes) were created to represent the curved portion of the parcel’s eastern boundary.
- Click the Editor menu > More Editing Tools > Advanced Editing.
- On the Advanced Editing toolbar that displays, click the Generalize tool.
- In the dialog box, for Maximum Allowable Offset, enter 2.
- Note: This value controls the degree to which the feature geometry will be simplified. For this example, an offset of 2 feet works well. When working with your own data, if you don’t like the result after generalizing, you can click Undo, then repeat the preceding steps and enter a different offset value until you find an acceptable value.
You see the selected feature, which has been generalized. The curved shape of the example parcel’s eastern boundary is still apparent.
- Double-click the feature to see its modified sketch.
Only six vertices are now used to represent the curve.
- Save your edits and stop editing.
If you have multiple features to generalize, you can select them all at once and use the Generalize tool as instructed above. To create a generalized output feature class from an existing feature class, use one of the generalization tools found in the ArcToolbox Data Management Tools toolbox.
To learn more ArcMap editing tips, join us this Thursday, November 20, for the Editing in ArcGIS 9: Tips and Tricks III live training seminar.
Colin Childs, an instructor with Esri Training Services, contributed this post.