What Is Gis

Simply put, a GIS combines layers of information about a place to give you a better understanding of that place. What layers of information you combine depends on your purpose--finding the best location for a new store, analyzing environmental damage, viewing similar crimes in a city to detect a pattern, and so on.

What is GIS?, PDF slide show, (1.89 MB)

Geography Matters, PDF white paper from ESRI (319 KB)

What do you need to use GIS?

A full GIS, or geographic information system, requires:

* Hardware (computers and peripherals)

* Software

* Data

* People

* Training

and sound analysis methods for interpreting the results generated by the GIS.

>> Read on for more detailed information.

How To Use GIS

Mapping Where Things Are

Mapping where things are lets you find places that have the features you are 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--By looking at the distribution of features on the map instead of just an individual feature, you can see patterns emerge.

This map shows the location of man-made objects such as buildings, antennas, and towers, as well as landscape features that can pose dangers to aircraft leaving or approaching airfields.

Map courtesy of General Command of Mapping Cartography Department, Ankara, Turkey.

[1] Mapping Where Things Are

[2] Mapping Quantities

[3] Mapping Densities

[4] Finding What's Inside

[5] Finding What's Nearby

[6] Mapping Change

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How To Use GIS

Mapping Quantities

People map quantities, such as 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.

For example, a catalog company selling children's clothes would want to find ZIP Codes not only around their store, but also those ZIP Codes with many young families with relatively high income. Or, public health officials might want not only to map physicians but also to map the numbers of physicians per 1,000 people in each census tract to see which areas are adequately served and which are not.

This map from the Silent Spring Institute of Newport, Massachusetts, shows the number of breast cancer cases in Cape Cod relative to land use. The map is used to analyze whether use of pesticides or other toxic chemicals may have contributed to the number of cases. Learn more about this study.

[1] Mapping Where Things Are

[2] Mapping Quantities

[3] Mapping Densities

[4] Finding What's Inside

[5] Finding What's Nearby

[6] Mapping Change

How to Do GIS Analysis

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 shows the potential acoustical impacts on the surrounding area of a particular type of rocket engine. The darker the blue, the higher the decibel level, to 129 decibels. 120 decibels or lower are acceptable outside the buffer zone (the jagged line surrounding the darker areas). Map courtesy of Lockheed Martin Space Operations, Stennis Space Center, Mississippi.

[1] How Do You Do GIS Analysis?

[2] Select Your Data

[3] Choose an Analysis Method

[4] Process the Data

[5] Look at the Results

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Why Use GIS?

1. Improve organizational integration.

2. Make better decisions.