Marble uses Qt's Model/View framework as a way to signal updates to a model to interested parts. In that respect, a Model class can wrap any possible data.
The Model-View framework is designed to hide the details of the model content, and to present it in a standardised way to views. The advantage of this solution is that the View need not know much about the data it presents.
The multiple models and proxies in Marble each fit the purpose of feeding some GeoData classes to interested widgets. Those models are fed by the FileManager.
Here is the list of Model and Proxy classes, and a description of how they are used.
It has signals/slots to react to files being added or removed in the FileManager.
It is used as the base model for GeoDataDocuments.
The KDescendantsProxyModel is used to flatten the tree of GeoData features. It represents the list of all Placemarks of all opened files.