What is GIS?
GIS allows us to view, understand, question, interpret, and visualize data in many ways that reveal relationships, patterns, and trends in the form of maps, globes, reports, and charts.
A GIS helps you answer questions and solve problems by looking at your data in a way that is quickly understood and easily shared.
GIS technology can be integrated into any enterprise information system framework.
Three Views of a GIS
A GIS is most often associated with a map. A map, however, is only one way you can work with geographic data in a GIS, and only one type of product generated by a GIS. A GIS can provide a great deal more problem-solving capabilities than using a simple mapping program or adding data to an online mapping tool (creating a “mash-up”).
A GIS can be viewed in three ways:
1. The Database View: A GIS is a unique kind of database of the world—a geographic database (geodatabase). It is an “Information System for Geography.” Fundamentally, a GIS is based on a structured database that describes the world in geographic terms.
2.The Map View: A GIS is a set of intelligent maps and other views that show features and feature relationships on the earth’s surface. Maps of the underlying geographic information can be constructed and used as “windows into the database” to support queries, analysis, and editing of the information.
3. The Model View: A GIS is a set of information transformation tools that derive new geographic datasets from existing datasets. These geoprocessing functions take information from existing datasets, apply analytic functions, and write results into new derived datasets.
By combining data and applying some analytic rules, you can create a model that helps answer the question you have posed. In the example below, GPS and GIS were used to accurately model the expected location and distribution of debris for the Space Shuttle Columbia, which broke up upon re-entry over eastern Texas on February 1, 2003
Together, these three views are critical parts of an intelligent GIS and are used at varying levels in all GIS applications.
What Can You Do with GIS?
Map Where Things Are
Mapping where things are lets you find places that have the features you’re looking for, and to see where to take action.
1. Find a feature—People use maps to see where or what an individual feature is.
2. Finding patterns—Looking at the distribution of features on the map instead of just an individual feature, you can see patterns emerge.
Maps of the locations of earthquake shaking hazards are essential to creating and updating building codes used in the United States. Online, interactive earthquake maps, as well as seismicity and fault data, are available at earthquake.usgs.gov.
People map quantities, like where the most and least are, to find places that meet their criteria and take action, or to see the relationships between places. This gives an additional level of information beyond simply mapping the locations of features.
Click to enlarge.This map shows the number of children under 18 per clinically active pediatrician for a particular study area. It was created by the Center for the Evaluative Clinical Sciences at Dartmouth Medical School as part of an effort to develop a national U.S. database of primary care resources and health services.
For example, a catalog company selling children’s clothes would want to find ZIP Codes not only around their store, but those ZIP Codes with many young families with relatively high income. Or, public health officials might not only want to map physicians, but also map the numbers of physicians per 1,000 people in each census tract to see which areas are adequately served, and which are not.
While you can see concentrations by simply mapping the locations of features, in areas with many features it may be difficult to see which areas have a higher concentration than others. A density map lets you measure the number of features using a uniform areal unit, such as acres or square miles, so you can clearly see the distribution.
Mapping density is especially useful when mapping areas, such as census tracts or counties, which vary greatly in size. On maps showing the number of people per census tract, the larger tracts might have more people than smaller ones. But some smaller tracts might have more people per square mile—a higher density.
This map shows population density in the east Asian and Indian Ocean regions.
Find What’s Inside
Use GIS to monitor what’s happening and to take specific action by mapping what’s inside a specific area. For example, a district attorney would monitor drug-related arrests to find out if an arrest is within 1,000 feet of a school–if so, stiffer penalties apply.
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This image from The Sanborn Map Company, Inc., shows a geoprocessed sample explosion radius around an area in California. Each separate zone represents 1/4-mile, the outermost perimeter being 1 mile away from the source.
Find What’s Nearby
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The Pacific Disaster Center has developed and applied a Vulnerability-Exposure-Sensitivity-Resilience model to map people and facilities (what’s nearby) exposed to flood risk in the Lower Mekong River Basin (the feature).
Map the change in an area to anticipate future conditions, decide on a course of action, or to evaluate the results of an action or policy.
1. By mapping where and how things move over a period of time, you can gain insight into how they behave. For example, a meteorologist might study the paths of hurricanes to predict where and when they might occur in the future.
2. Map change to anticipate future needs. For example, a police chief might study how crime patterns change from month to month to help decide where officers should be assigned.
3. Map conditions before and after an action or event to see the impact. A retail analyst might map the change in store sales before and after a regional ad campaign to see where the ads were most effective.
These images are from a poster titled “Losing Cape Cod,” which is distributed by the Woods Hole Research Center in Woods Hole, Massachusetts. The poster shows the severe change in land use on Cape Cod since 1951. The image on the left shows the town of Barnstable in 1951 and the image on the right shows Barnstable in 1999.
Answering Questions with GIS
GIS is fundamentally used to answer questions and make decisions. To use GIS properly, it is important to know what you want to ask and follow a disciplined process for getting the answer.
1. Frame the question.
Start your GIS analysis by figuring out what information you need. This is most often in the form of a question:
* Where were most of the burglaries last month?
* How much forest is in each watershed?
* Which parcels are within 500 feet of this liquor store?
Be as specific as possible about the question you want to answer. This will help you decide how to approach the analysis, which method to use, and how to present the results.
This map was used to answer the question “Where is the best place to land a Mars Exploration Rover?” Learn more.
2. Select your data.
The type of data and features you work with help determine the method you use. Or, if you know you need to use a specific method to answer your question, you may find you need additional data.
Data can come from any number of sources—databases within your organization, contact managers, CAD files, the Internet, commercial data providers, government organizations, and so on.
The data you choose and where you get it depends on your needs and budget. Most critical is that the data be good quality, accurate data.
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This water utility map shows five sets of data: parcels, building footprints, grid lines, streets, and pipes color coded by replacement status. Only the data necessary for understanding pipe locations and status was displayed. Learn more.
Learn more about data types, data models, and sources of data.
3. Choose an analysis method.
Decide which analysis method to use based on your original question and how the results of the analysis will be used.
For example, if you are doing a quick study of burglaries in a city to look for patterns, you might just map the individual crimes and look at the maps. If the information will be used as evidence in a trial, however, you might want a more precise measure of the locations and numbers of assaults for a given time period.
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This seismicity map shows the time dependent relation between the inception of geothermal power production and the occurrence of earthquake activity from 1967 through 1995 in Santa Rosa, Califorina. This study used temporal analysis as the analysis method of choice. Learn more about the study.
4. Process the data.
Once you’ve selected the analysis method, you’ll need to process your data in a way that makes sense for your goal.
If you are mapping where things are located, you may need to assign geographic coordinates, such as latitude and longitude or address, to your data and assign category values to the data.
If you are mapping quantities, such as number of vegetation types in a state park, you may need to choose a classification scheme and decide on how many classes to represent your data.
If you are trying to find out what is inside, you may need to measure an area or combine different layers of information.
5. Look at the results.
The final step is to look at the results of your analysis and take action based on those results.
Your results can be displayed as a digital map, printed as a paper map, combined with spreadsheet-like tables or charts, or displayed as such. Though a lot of emphasis in GIS is in making maps, the software is flexible enough to allow you to display your results in the format that best suits your needs.
Accoustical impacts of a rocket engine
This map was created to locate explosive remnants of war in Iraq to help in planning the cleanup effort. Learn more.