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A GIS is a computer system capable of capturing, storing, analyzing, and displaying geographically referenced information. A GIS operator can look at various types of data for a specific area and analyze them in order to make intelligent decisions.

A GIS can be used for scientific studies, resource management, and development planning. For example, a GIS might assist climatologists in determining areas where sea level rise will be the most disruptive, where desertification is spreading, how much impact El Niño is having, and the spatial relationships between drinking water, heat waves, drought, and disease.

The power of a GIS comes from its ability to relate different information in a spatial context and to reach a conclusion about that relationship. Most geographic information has a locational reference, which makes it spatial; that is, it fits somewhere on the Earth.

When data are collected by field scientists, they can be mapped or put in some kind of spatial reference system, such as a latitude and longitude coordinate system or any other map projection. When diverse data are all projected into the same system, that data can be overlaid and the layers analyzed in relation to other data concerning the same parcel of land in order to identify conflicts, problems, patterns, and relationships. For example, if a climatologist were interested in tracking the effects of global warming, all the pertinent spatial data involved could be reviewed, such as availability of water, shortage of food, vegetation cover, rainfall amounts, temperature patterns, disease outbreaks, ecosystem change, population densities, and natural resource inventories.

A GIS can convert existing digital information, which may not yet be in map form, into forms it can recognize and use. Digital satellite images can be analyzed to produce a map of digital information about land use and land cover. A GIS can also convert tabular data into a maplike form that a GIS can recognize.

There are several ways to enter data into an operable GIS system. Features on existing paper maps can be digitized by hand-tracing with a computer mouse on a computer screen or on a digitizing tablet to collect the coordinates of features. Scanners can convert maps to a digital product. Data collected from a global positioning system (GPS) can also be incorporated into a GIS. Data capture involves identifying objects on a map, their coordinate locations on the Earth's surface, and their spatial relationships. Many software programs have been developed to automatically extract features from remote sensing imagery.

Objects are identified in a series of attribute tables (the information part of a GIS). Spatial relationships, such as whether features intersect, are adjacent, or are separate from each other, are the key to all GIS-based analysis. This enables Earth scientists to look at many variables related to an area and study cause, effect, and interactions and allows scientists to better study variables that may not have obvious correlations. Looking at data on wildlife habitat and comparing it to the availability of food, existing habitat, and migration opportunities, for example, gives scientists insights about the way global warming may affect wildlife.

One of the key requirements of a GIS is the maintenance of data consistency and integrity. Data may originally be collected at different scales or in varied formats. The GIS must convert these data sets into a compatible format, such as a common map projection. Data must also be accurate. If data entered into a GIS is of high quality, then the output

Global Warming Trends

© Info base Publishing o Water Q Vegetation © Geology Q Temperature Q Population Q Streams

© Info base Publishing o Water Q Vegetation © Geology Q Temperature Q Population Q Streams

Multiple layers of information can be stacked in a GIS to analyze how different components of the landscape affect each other. One GIS application is to model sea-level rise and its effects on major coastal areas worldwide.

from GIS analysis will be high quality; the final product is only as good as its least accurate input.

One tremendous achievement of GIS systems in recent years is their ability to model data to predict two- and three-dimensional characteristics of the Earth's surface, subsurface, and atmosphere, from which working models of cause and effect can be created. This real-life advantage allows scientists to check possible interactions and relationships of diverse phenomena and make intelligent decisions concerning them.

A GIS can recognize and analyze spatial relationships among mapped phenomena. Conditions of adjacency (what is next to what), containment (what is enclosed by what), and proximity (how close something is to something else) can be determined with a GIS.

A critical component of a GIS is its ability to produce graphics on a screen or on paper to convey the results of analysis. Wall maps, Internet maps, interactive maps, and other graphics can be generated to enable decision makers to visualize and understand the results of the analysis and simulations of potential events. The illustration on page 141 depicts the basic architecture of a GIS and how multiple layers can be stacked to make detailed analyses of the land and Earth systems as well as how an application to model sea-level rise can be used to determine how areas will be affected if ice caps and glaciers melt. In this example, the Florida Bureau of Geology and the USGS Geologic Division mapped the areas during the last interglacial period, when the global climate was warmer than today. The sea level then was 23 to 26 feet (7-8 m) higher than it is today. Climatologists believe these earlier sea levels may be reached again if global warming continues. Wildlife habitats such as the Everglades and other key features that affect the lives of more than 7 million residents of Florida would be negatively affected if this occurred. Using GIS, these impacts can be modeled and give not only scientists a clear view of the consequences of global warming, but also politicians, planners, environmentalists, and the population in general, showing why it is so important for everyone to become familiar with the realities of global warming and climate change.

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