I know def queries quite well, but what's this Display Filter thing? Is it just combining the visible scale with a def query?
Yes. They are very handy for authoring multiscale maps since you don't have to make copies of layers just to show different features at different scales.
Display filters—ArcGIS Pro | ArcGIS Desktop
Author a multiscale map—ArcGIS Pro | ArcGIS Desktop
Display filter simply filters what is displayed on the screen dependent upon the settings configured for the feature. The feature data is still available and will show in attribute tables, can be used in calculations, selections can be made, etc.
Whereas a definition query removes the data as if it does not exist. It does not show in the attribute tables nor can it be accessed for calculations or other processes without removing the definition query for that feature layer.
yes, included in that "etc" is selections! Even when you can't see features due to display filter settings, you can still select them. That is not true when working with def queries.
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