A geographic information system (GIS) is a computer system for capturing, storing, checking, and displaying data related to positions on Earth’s surface. By relating seemingly unrelated data, GIS can help individuals and organizations better understand spatial patterns and relationships.
 
GIS technology is a crucial part of spatial data infrastructure, which the White House defines as “the technology, policies, standards, human resources, and related activities necessary to acquire, process, distribute, use, maintain, and preserve spatial data.”
 
GIS can use any information that includes location. The location can be expressed in many different ways, such as latitude and longitude, address, or ZIP code. 
 
Many different types of information can be compared and contrasted using GIS. The system can include data about people, such as population, income, or education level. It can include information about the landscape, such as the location of streams, different kinds of vegetation, and different kinds of soil. It can include information about the sites of factories, farms, and schools; or storm drains, roads, and electric power lines.
 
With GIS technology, people can compare the locations of different things in order to discover how they relate to each other. For example, using GIS, a single map could include sites that produce pollution, such as factories, and sites that are sensitive to pollution, such as wetlands and rivers. Such a map would help people determine where water supplies are most at risk.
 
Data Capture
 
Data Formats
GIS applications include both hardware and software systems. These applications may include cartographic data, photographic data, digital data, or data in spreadsheets.
 
Cartographic data are already in map form, and may include such information as the location of rivers, roads, hills, and valleys. Cartographic data may also include survey data, mapping information which can be directly entered into a GIS. 
 
Photographic interpretation is a major part of GIS. Photo interpretation involves analyzing aerial photographs and assessing the features that appear.
 
Digital data can also be entered into GIS. An example of this kind of information is computer data collected by satellites that show land use—the location of farms, towns, and forests.
 
Remote sensing provides another tool that can be integrated into a GIS. Remote sensing includes imagery and other data collected from satellites, balloons, and drones.
 
Finally, GIS can also include data in table or spreadsheet form, such as population demographics. Demographics can range from age, income, and ethnicity to recent purchases and Internet browsing preferences.
 
GIS technology allows all these different types of information, no matter their source or original format, to be overlaid on top of one another on a single map. GIS uses location as the key index variable to relate these seemingly unrelated data. 
 
Putting information into GIS is called data capture. Data that are already in digital form, such as most tables and images taken by satellites, can simply be uploaded into GIS. Maps, however, must first be scanned, or converted to digital format.
 
The two major types of GIS file formats are raster and vector. Raster formats are grids of cells or pixels. Raster formats are useful for storing GIS data that vary, such as elevation or satellite imagery. Vector formats are polygons that use points (called nodes) and lines. Vector formats are useful for storing GIS data with firm borders, such as school districts or streets.
 
Spatial Relationships
GIS technology can be used to display spatial relationships and linear networks. Spatial relationships may display topography, such as agricultural fields and streams. They may also display land-use patterns, such as the location of parks and housing complexes.
 
Linear networks, sometimes called geometric networks, are often represented by roads, rivers, and public utility grids in a GIS. A line on a map may indicate a road or highway. With GIS layers, however, that road may indicate the boundary of a school district, public park, or other demographic or land-use area. Using diverse data capture, the linear network of a river may be mapped on a GIS to indicate the stream flow of different tributaries. 
 
GIS must make the information from all the various maps and sources align, so they fit together on the same scale. A scale is the relationship between the distance on a map and the actual distance on Earth. 
 
Often, GIS must manipulate data because different maps have different projections. A projection is the method of transferring information from Earth’s curved surface to a flat piece of paper or computer screen. Different types of projections accomplish this task in different ways, but all result in some distortion. To transfer a curved, three-dimensional shape onto a flat surface inevitably requires stretching some parts and squeezing others. 
 
A world map can show either the correct sizes of countries or their correct shapes, but it can’t do both. GIS takes data from maps that were made using different projections and combines them so all the information can be displayed using one common projection. 
 
GIS Maps
 
Once all of the desired data have been entered into a GIS system, they can be combined to produce a wide variety of individual maps, depending on which data layers are included. One of the most common uses of GIS technology involves comparing natural features with human activity.
 
For instance, GIS maps can display what manmade features are near certain natural features, such as which homes and businesses are in areas prone to flooding.
 
GIS technology also allows to “dig deep” in a specific area with many kinds of information. Maps of a single city or neighborhood can relate such information as average income, book sales, or voting patterns. Any GIS data layer can be added or subtracted to the same map. 
 
GIS maps can be used to show information about numbers and density. For example, GIS can show how many doctors there are in a neighborhood compared with the area’s population. 
 
With GIS technology, researchers can also look at change over time. They can use satellite data to study topics such as the advance and retreat of ice cover in polar regions, and how that coverage has changed through time. A police precinct might study changes in crime data to help determine where to assign officers. 
 
One important use of time-based GIS technology involves creating time-lapse photography that shows processes occurring over large areas and long periods of time. For example, data showing the movement of fluid in ocean or air currents help scientists better understand how moisture and heat energy move around the globe.
 
GIS technology sometimes allows users to access further information about specific areas on a map. A person can point to a spot on a digital map to find other information stored in the GIS about that location. For example, a user might click on a school to find how many students are enrolled, how many students there are per teacher, or what sports facilities the school has. 
 
GIS systems are often used to produce three-dimensional images. This is useful, for example, to geologists studying earthquake faults. 
 
GIS technology makes updating maps much easier than updating maps created manually. Updated data can simply be added to the existing GIS program. A new map can then be printed or displayed on screen. This skips the traditional process of drawing a map, which can be time-consuming and expensive.
 
GIS Jobs
 
People working in many different fields use GIS technology. GIS technology can be used for scientific investigations, resource management, and development planning.
 
Many retail businesses use GIS to help them determine where to locate a new store. Marketing companies use GIS to decide to whom to market those stores and restaurants, and where that marketing should be.  
 
Scientists use GIS to compare population statistics to resources such as drinking water. Biologists use GIS to track animal migration patterns. 
 
City, state, or federal officials use GIS to help plan their response in the case of a natural disaster such as an earthquake or hurricane. GIS maps can show these officials what neighborhoods are most in danger, where to locate emergency shelters, and what routes people should take to reach safety. 
 
Engineers use GIS technology to support the design, implementation, and management of communication networks for the phones we use, as well as the infrastructure necessary for Internet connectivity. Other engineers may use GIS to develop road networks and transportation infrastructure.
 
There is no limit to the kind of information that can be analyzed using GIS technology.
GIS (geographic information system)
GIS allows multiple layers of information to be displayed on a single map.

Earth Science Information Center
To find out more about how GIS is used in your local community, contact your nearest Earth Science Information Center (ESIC). Staff from the US Geological Survey (USGS) answer questions about aerial photographs, maps, satellite imagery, computer programs, data formats, data standards, and digital cartographic data. To contact your local ESIC, call 1-888-ASK-USGS or visit the website.

Photozincography
The labor-intensive process of photozincography anticipated GIS in the 19th century. This process used zinc plates to draft different layers of a map, and a large-process camera to combine the layers into a single image.
Neogeography
Neogeography is a controversial term that often describes user-generated location data or “citizen geographer” platforms. Neogeography may describe projects as varied as the massive collaborative effort of OpenStreetMap and auto-generated location tags in social media.
accomplish
Verb

to succeed or complete a goal.

aerial photograph
Noun

picture of part of the Earth's surface, usually taken from an airplane.

align
Verb

to put in a straight line.

assess
Verb

to evaluate or determine the amount of.

assign
Noun

to give or distribute.

biologist
Noun

scientist who studies living organisms.

Noun

natural or artificial line separating two pieces of land.

Noun

line separating geographical areas.

cartographic
Adjective

having to do with maps and mapmaking.

crime
Noun

unlawful activity.

crucial
Adjective

very important.

Noun

steady, predictable flow of fluid within a larger body of that fluid.

data
Plural Noun

(singular: datum) information collected during a scientific study.

data capture
Noun

process of putting information into a geographic information system (GIS).

demographic
Adjective

having to do with the social characteristics and statistics of a population.

Noun

number of things of one kind in a given area.

development
Noun

construction or preparation of land for housing, industry, or agriculture.

digital
Adjective

having to do with numbers (or digits), often in a format used by computers.

distortion
Noun

representation that is twisted, mistaken, or false.

drone
Noun

unmanned aircraft that can be guided remotely.

earthquake
Noun

the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

Noun

height above or below sea level.

engineer
Noun

person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).

enroll
Verb

to enter or participate.

ethnicity
Noun

identity in a group sharing genetic characteristics, culture, language, religion, or history.

expensive
Adjective

very costly.

facility
Noun

a building or room that serves a specific function.

factory
Noun

one or more buildings used for the manufacture of a product.

farm
Noun

land cultivated for crops, livestock, or both.

fault
Noun

a crack in the Earth's crust where there has been movement.

federal
Adjective

having to do with a nation's government (as opposed to local or regional government).

Noun

overflow of a body of water onto land.

forest
Noun

ecosystem filled with trees and underbrush.

Noun

any system for capturing, storing, checking, and displaying data related to positions on the Earth's surface.

geologist
Noun

person who studies the physical formations of the Earth.

grid
Noun

horizontal and vertical lines used to locate objects in relation to one another on a map.

hardware
Noun

computer machinery.

heat energy
Noun

a form of energy that is transferred by a difference in temperature

Noun

land that rises above its surroundings and has a rounded summit, usually less than 300 meters (1,000 feet).

hurricane
Noun

tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region.

income
Noun

wages, salary, or amount of money earned.

inevitable
Adjective

certain to happen, unavoidable.

infrastructure
Noun

structures and facilities necessary for the functioning of a society, such as roads.

instream flow
Noun

measure of the cubic feet per second of water flowing in a specific area of a stream at a specific time.

Internet
Noun

vast, worldwide system of linked computers and computer networks.

Noun

the geographic features of a region.

land use
Noun

range of purposes people put to the earth.

Noun

distance north or south of the Equator, measured in degrees.

Noun

position of a particular point on the surface of the Earth.

Noun

distance east or west of the prime meridian, measured in degrees.

manipulate
Verb

to manage a complex device or situation with great skill.

Noun

symbolic representation of selected characteristics of a place, usually drawn on a flat surface.

map projection
Noun

method by which shapes on a globe are transferred to a flat surface.

marketing
Noun

art and science of selling a product.

Noun

movement of a group of people or animals from one place to another.

moisture
Noun

wetness.

natural disaster
Noun

an event occurring naturally that has large-scale effects on the environment and people, such as a volcano, earthquake, or hurricane.

Noun

an area within a larger city or town where people live and interact with one another.

node
Noun

beginning or ending point of an edge, arc or network of lines.

pixel
Noun

smallest part of an image displayed on an electronic screen.

polar
Adjective

having to do with the North and/or South Pole.

Noun

introduction of harmful materials into the environment.

polygon
Noun

geometric figure having three or more straight sides. In GIS, a closed shape on a map defined by a connected sequence of x, y coordinate pairs.

population
Noun

total number of people or organisms in a particular area.

power grid
Noun

network of cables or other devices through which electricity is delivered to consumers. Also called an electrical grid.

power line
Noun

cable or cord used to transfer electricity from a power plant to a population center. Also called a transmission line.

projection
Noun

flat representation of a sphere.

prone
Adjective

vulnerable or tending to act in a certain way.

raster data
Noun

spatial information organized as collections of cells that represent groups of data, such as elevations.

remote sensing
Noun

methods of information-gathering about the Earth's surface from a distance.

resource management
Noun

art and science of directing or negotiating the way people interact with the natural landscape. Also called natural resource management.

retail
Adjective

having to do with the sale of finished goods to consumers.

Noun

large stream of flowing fresh water.

road
Noun

path, usually paved, for vehicles to travel.

route
Noun

path or way.

satellite
Noun

object that orbits around something else. Satellites can be natural, like moons, or made by people.

satellite imagery
Noun

photographs of a planet taken by or from a satellite.

scale
Noun

relationship between distances shown on a map and actual distances.

scan
Verb

to transfer data, usually visual, on to a computer.

school district
Noun

geographic area whose schools are managed by one administration.

software
Noun

electronic programs of code that tell computers what to do.

soil
Noun

top layer of the Earth's surface where plants can grow.

spatial data
Noun

information used to pose, analyze, and resolve problems about the Earth's surface that reflect environmental and human processes.

storm drain
Noun

system to empty streets of excess rainwater. Storm drains flow into local creeks, rivers, or seas.

survey data
Noun

information gained from precisely measuring the surface of the land.

technology
Noun

the science of using tools and complex machines to make human life easier or more profitable.

three-dimensional
Adjective

having the appearance of width, height, and depth.

time-lapse photography
Noun

photographing of a slow and continuous process at regular intervals, for projection at a higher speed.

topography
Noun

study of the shape of the surface features of an area.

town
Noun

human settlement larger than a village and smaller than a city.

Noun

stream that feeds, or flows, into a larger stream.

upload
Verb

to transfer electronic information from a smaller computer to a larger computer.

valley
Noun

depression in the Earth between hills.

vector data
Noun

information representing the precise location in terms of a point, line or a shape.

vegetation
Noun

all the plant life of a specific place.

voting pattern
Noun

general way a specific population votes in political elections.

Noun

area of land covered by shallow water or saturated by water.

ZIP code
Noun

(zone improvement plan) series of numbers used to help locate an address for mail delivery.