Defines which observations are returned from the service. Use this property to define a filter that informs the server which observations to send on the stream. The filter may include spatial or attribute criteria (or both). Using this server-side filter is useful for limiting how much data must be handled in the client application, which can help with application performance and memory footprint.

This property is used when the data source connection is initiated; therefore, the filter cannot be changed once the data source is loaded.

The default value is null, meaning no filter is applied.