Feature retrieval

Feature layers within the ArcGIS Viewer for Silverlight can be configured to specify the mode used to retrieve features. You can retrieve all the features in a layer at once or only retrieve features within the current extent. The two options are described as follows:

• Retrieve features within the current extent (default)—Retrieves features as they are needed, requesting only the features within the current map extent. As the map extent is changed, the features within the new extent are requested and drawn on the map. Features that were previously retrieved remain in the layer. While this method of feature retrieval requires more round trips between the client and server, it has the advantage that only the features needed for map display are downloaded.
• Retrieve all features—Retrieves all the features from the layer immediately after the layer is added to the map. This eliminates any need to return to the server for information but can encounter performance problems if the layer contains many features and the map extent is such that many features are visible at one time. Additionally, the number of features in the layer may exceed the maximum number that can be returned by the server in one request. When this is the case, the features beyond the limit are not included in the layer. By default, feature layers in ArcGIS Server 9.3.1 return a maximum of 500 features in one request. Feature layers in ArcGIS Server 10 and later return 1,000 features in one request by default. These defaults can be changed by the server administrator.

You can configure feature retrieval for a layer as follows:

1. Open the Configure Layers panel and select the layer to be configured.
2. Right-click the layer and click Configure. Alternatively, click the Configure button at the bottom of the Configure Layers panel:
3. On the Configuring panel that appears, expand the Feature Retrieval group:
   • Select Get features within map area to enable retrieval of features within the current extent.
   • The Cache Size defines the maximum number of features the layer can retain. When the map extent is changed, features within the new extent are retrieved, and features that have previously been requested are retained. However, if the number of features in the layer exceeds the value defined for cache size, features will be removed from the layer to bring the number of features within the cache size value range. When this occurs, the oldest features are removed first.
     Note:

     Features are only removed from the layer on the client; the data on the server remains unchanged.