QGeoPositionInfoSource: What and where are the system's default "sources of location data"?

The following quote is from t开发者_如何学Pythonhis link: http://apidocs.meego.com/1.2-preview/qtmobility/qgeopositioninfosource.html#createDefaultSource

Creates and returns a position source with the given parent that reads from the system's default sources of location data, or the plugin with the highest available priority.

What and where are the system's default "sources of location data"? Any examples? And what do I need to read to understand these concepts?

The default source depends on the Device. As to the question regarding what the sources might be , here is an extract from forum.nokia documentation regarding symbian phones , although this is mostly true in reference to other devices and platforms as well

GPS based: It can provide location estimation with accuracy from 10 to 30 meters. Depending on the actual technology and the state of GPS module, time to first fix varies from several seconds to minutes. Time to next fix is normally 1 second. It may not work indoor. The GPS module, which makes location estimation, may reside internally (e.g. integrated GPS) or externally (e.g. Bluetooth GPS) of the terminal.

Assisted GPS: Assisted GPS technology improves performance (i.e. time to first fix and sensitivity) by acquiring assistant data from an assistance server. The mobile phone receives the assistant data from wireless network. Depends on the operator and subscription, end user may have to pay for receiving assistant data.

Network based: It can provide location estimation with accuracy from a hundred meter to several kilometers. Time to first fix and time to next fix is normally within 10 seconds. It works also indoor. It normally requires support from operator.