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Quantum GIS: What is GIS?

What is GIS?

Geographic information systems (GIS) are used in a wide range of academic and applied fields. Simply put, GIS allows you to combine tabular data (e.g. spreadsheet sheet) with a geographic boundaries (e.g. maps).

Examples

Maantay, J. (2007). Asthma and air pollution in the Bronx: Methodological and data considerations in using GIS for environmental justice and health research. Health & Place, 13(1), 32-56.
Mapped residences of asthma patients based on recorded addresses (geocoding) and determined whether they were more likely to live near pollution sources (buffers, proximity analysis).

Greater Philadelphia GeoHistory Network.

Larsen, K., & Gilliland, J. (2008). Mapping the evolution of “food deserts” in a Canadian city: Supermarket accessibility in London, Ontario, 1961–2005. International Journal of Health Geographics, 7(16), n.p.
Mapped the location of grocery stores from addresses (geocoding), determined how many people lived with a 10-minute bus ride from the stores (network analysis).

Jones, E. E. (2006). Using Viewshed Analysis to Explore Settlement Choice: A Case Study of the Onondaga Iroquois. American Antiquity, 71(3), 523-538.
Used the topography around Iroquois archaeological sites to determine how far villager inhabitants could see (viewshed analysis).

For more examples, search Esri's GIS Bibliography.

What is QGIS?

QGIS (or Quantum GIS) is an open source geographic information system, meaning that it can be downloaded and installed on your desktop free of charge. It runs on Windows, Mac OS X, and Linux. There are also numerous plug-ins that extend the functionality of QGIS.

Common functions

Geocode: To create points on a map from street addresses in spreadsheet form

Overlay: To superimpose two or more maps or layers in the same coordinate system, to show the relationships between them

Georeference: To align geographic data (map, layer, etc.) with a given coordinate system, allowing for overlays

Select by location (proximity analysis): To select features according to their relationship in space to other features

Select by attribute: To select features according to their properties (attributes), like querying a database

Buffer: To create a zone around a feature in units of distance or time

Network analysis: To find the distance from a feature travelled along a network (such as roads, public transit) rather than as the crow flies

Join: To attach fields from one table to those of another through an attribute or field common to both tables.

Viewshed analysis: To determine what areas are visible from a particular location.

Adapted from Esri's GIS Dictionary.