A geographic information system (GIS) is fundamentally a functional assortment of software that interfaces with a computer for the purpose of addressing spatial issues. The term geographic can be broken down into two basic elements: geo is Earth-related, and graphic means to describe or depict the Earth through maps or drawings. Information is data with explanation; or data in an applied sense. Information can be word-based or graphic and it is derived from data elements through a process of thought, observations, and measurement. Data consist of measured phenomena, statistics, or other quantitatively derived values. A system is basically an assemblage of connected components or activities which, when linked together, interact as a functional unit.
A Brief History of GIS
The GIS began when land inventory scientists formed the Canadian Geographic Information system in 1963. At around the same time (1963) the Urban and Regional Information Systems Association (URISA) was developed in the United States. In 1964 Harvard University established the Laboratory for Computer Graphics and Spatial Analysis. A private research company named the Environmental Systems Research Institute (ESRI) became the largest GIS software developer and distributor in the world. In 1981, the first major commercial GIS software (ArcInfo) was launched from ESRI. Many advances in software applications, research design, and the entry of commercial, private, and government agencies into GIS followed. In 1995, the United States Department of Defense introduced the NAVigation System with Time and Ranging (NAVSTAR) program. Accurate location of any area on Earth became possible to derive from signals transmitted from satellites to a new receiving instrument called a global positioning system (GPS). The introduction of GPS and GIS technologies revolutionized the way the planet was mapped, and by extension, the methods of spatial (Earth area) analysis became much more powerful with the introduction of computer-assisted applications. The word geomatics is often used as an umbrella term for a professional discipline that is a combination of automated (computer) cartography, remote sensing, digital image processing, geographic information systems, and GPS.
Geography as a Spatial Discipline
Geography is a spatial discipline that seeks to link, understand, and explain associations and inter-relationships expressed by similarity, difference, or uniqueness of physical and human dimensions operating in areas or places on the planet. Traditionally, most sciences and other fields of knowledge are fragmented into narrow, content-oriented themes such as biology, chemistry, physics, economics, and sociology. Geography has no specific segment of knowledge upon which it focuses, but rather uses all available knowledge, typically in the spatial domain. Geography organizes and integrates diverse knowledge to understand relationships between features found in and between places, as well as determine and understand active processes that operate to create those relationships. Geography is often thought of as an integrative discipline that brings together a study of relationships between and among people, places, and natural the environment from an area or spatial perspective. History is like geography in the sense it has no specific segment of knowledge upon which it focuses, rather it all knowledge, but viewed in a time-perspective to understand human and physical inter-relationships and processes.
Earth feature relationships are distributed throughout space and time, and the study of them is appropriately called spatial analysis. Space can be thought of as a container; therefore, all objects that take up space will have location, distance, direction, pattern, shape, and size characteristics . Spatial analysis is fundamental to all of geography and is important in many other disciplines. As a method of inquiry, any analysis must begin with a curiosity for the world in which we live. This should lead to developing questions followed by a collection of data. Information results when data applicable for resolving a question or problem is identified. Analysis of data that have spatial attributes is accomplished using a geographic information system.
A GIS provides the platform to most effectively perform spatial analysis that can ultimately lead to understanding relationships, interactions, and processes within and between physical (e.g. soil, rock, plants, water, etc.) and social/cultural-economic (e.g. humans and their activities, economic features) elements found on Earth. A GIS can serve as an instrument use in activities such as decision-making, solving spatial problems, or support planning for the future (e.g. urban-regional planning, Earth resources planning, environmental planning).
Characteristics of a Geographic Information System
GIS software and computer hardware collectively provide a mechanism by which spatial objects (objects with known location on Earth) can be linked to data (a database file which in this context it would be listed in table or tabular format) consisting of data/information that describes the nature of these spatial objects. Spatial (area represented in digital form) and tabular data may be input and stored, retrieved, updated, manipulated, deleted, analyzed, and output in graphic and tabular format. A GIS functions as a spatial database management, and analysis system. Maps, tables, charts, images, and other spatial models are generated from spatial and tabular data as a means for identifying trends, likeness, difference, and anomalies associated with Earth features.
Spatial objects are formed by graphic elements expressed as points, lines, and/or polygons. Points can represent location information such as objects of interest (schools, churches, cemeteries, etc.). Lines may represent transportation networks such a roads, railroads, streams, etc. Polygons are any object that possesses area such as town and city boundaries, parks, national forests, etc. When combined on a map, these spatial elements represent "real world" phenomena.
The power of a GIS resides in its ability to link all spatial elements with a geographic coordinate reference system such as latitude and longitude for comparative purposes. There are other methods to establish a geographic reference system (e.g. State Plane Coordinate System, Universal Transverse Coordinate System). When spatial data are linked to a common grid or coordinate system, the term georeferenced is used. Relationships among and between graphic elements, including connectivity, adjacency, orientation and containment can be made when spatial information is georeferenced. Spatial analysis can be performed with reference to size, shape, location, distance, and direction of Earth objects.
A GIS provides a dynamic means of associating spatial and tabular data/information through thematic (e.g. soils, average income, topography) layers. Dynamic implies that the thematic content may be changed or upgraded. In addition, queries (questions) may be input into a GIS in which only selected segments of a database are combined with specific spatial objects. The GIS can generate a completely new configuration for these spatial objects and their associated database through structured queries, which creates output in the form of maps, tables and graphs.
To summarize, a GIS is in part a technology employed to design and construct maps and in part an analytic tool focusing on spatial relationships. Maps are considered a means to convey graphical/area information. A GIS has qualities of science which serve as a means of integrating graphical information derived from supporting disciplines. A GIS functions as a major tool/technique that links physical and socio-economic elements found in a world society. A GIS enables an understanding of place as a physical location identifiable through a georeference system, which, by extension, establishes spatial boundaries for features of interest. When combined with the human and physical dimensions characteristic of a particular location, a GIS aids in identifying a geographic region and the processes at work in a defined region. Processes are interrelated actions operating on Earth features that produce or prevent changes in our environment throughout time and at varied scales.