Quantum GIS

Quantum GIS (often abbreviated to QGIS) is a free software desktop Geographic information systems (GIS) application that provides data viewing, editing, and analysis capabilities.

Development
Gary Sherman began development of Quantum GIS in early 2002, and it became an incubator project of the Open Source Geospatial Foundation in 2004. Version 1.0 was released in January 2009.

Quantum GIS is written in C++, and its GUI uses the Qt library. Quantum GIS allows integration of plug-ins developed using either C++ or Python. In addition to Qt, required dependencies of Quantum GIS include GEOS and SQLite. GDAL, GRASS GIS, PostGIS, and PostgreSQL are also recommended.

Quantum GIS is a multi-platform application and runs on different operating systems including Mac OS X, Linux, UNIX, and Microsoft Windows. For Mac users, the advantage of Quantum GIS over GRASS GIS is that it does not require the X11 windowing system in order to run, and all around the interface is much cleaner and faster. Quantum GIS can also be used as a graphical user interface to GRASS. Quantum GIS has a small file size compared to commercial GISs and requires less RAM and processing power; hence it can be used on older hardware or running simultaneously with other applications where CPU power may be limited.

Quantum GIS is continually maintained by an active group of volunteer developers who regularly release updates and bug fixes. Currently, developers have converted Quantum GIS into 14 languages and the application is used internationally in academic and professional environments.

Licensing
Because it is distributed as a free software application under the GNU distribution license, Quantum GIS can be reprogrammed to perform different or more specialized tasks. There are also plug-ins available to expand compatibility and functionality.

Data formats
Quantum GIS allows use of Esri's proprietary shapefile format and coverages. Many other formats are supported via OGR, including ESRI Personal Geodatabases and File Geodatabases (requires GDAL/OGR 1.9). However, mailing list remarks indicate that on Linux, the MSAccess-based Personal Geodatabase format may not work. MapInfo, PostGIS, and a number of other formats are supported in Quantum GIS. Web services, including Web Map Service and Web Feature Service, are also supported to allow use of data from external sources.

Functionality
Quantum GIS provides integration with other open source GIS packages, including PostGIS, GRASS, and MapServer to give users extensive functionality.