Marble uses Qt's Model/View framework as a way to signal updates in a model to interested parts. In that respect, a Model class can wrap any possible data.
Here is the list of Model classes, and a description of how they are used.
It is used by the DataViewPlugin debug plugin (and is broken atm).
It represents a list of gpx data files represented as GpxFile
This was originally intended to but used as the model for the File List View ( which is accessible by running marble with --enableFileView ) but has since been replaced by the FileViewModel.
The model is used as a member in the GpsLayer to hold the list of gpx files as a collection class and is deprecated. This, along with the whole current GPX implementation, needs to be removed and updated to the current concepts in Marble. See Gpx Status
It is used by the GeoRenderPlugin to access the list of vector data and draw it.
It represents the list of opened files. The FileManager signals it about the documents it opens or closes.
It is used by no other code.
It represents a list of Placemarks.
The MarbleRunnerManager appends the list of placemarks that the Runners found in its instance.
It is used by the MarbleControlBox to provide a list of placemarks (either from the PlacemarkManager or from the MarbleRunnerManager).
It is also used by the PlacemarkLayout to determine layouting on the map.