If the DialogType property is configured to Map, the DialogData should refer to the data item to which the geography data is configured (feature-attribute). This is needed to inform the GeoDMS how to visualise the geography domain unit of the requested data item.
The DialogData property can also be configured for a values-unit describing the how-to-configure-a-coordinate-system used for map views. In that case the DialogData can be configured with one or multiple attribute(s) referring to geographic information. These attribute will then be grouped into a background layer that is by default presented in each map view.
If the feature attribute is called (G)(g)eometry, this property does not have to be configured (since version 7.206).