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 can use any information that includes location. The location can be expressed in many different ways, such as latitude and longitude or address.

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 different kinds of vegetation and soil. It can include information about the sites of factories, farms and schools or about storm drains, roads and electric power lines.

With GIS technology, people can compare the locations of different things 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.

However, there are challenges to GIS technology. While the cost of GIS has decreased in recent years with the adoption of cloud-based data storage solutions, the technology is still expensive to set up and maintain, limiting its accessibility in communities with lower budgets. It can also be difficult to learn how to use the system and often requires training. Sometimes the information collected by these systems is so complex, it’s hard to integrate and interpret the data. Using old or inaccurate data can introduce inaccuracies and create technical challenges.

Citizen users can present benefits and challenges. Users who are not GIS experts, sometimes called citizen geographers, provide on-the-ground information to these systems. This first-hand information can help solve problems quickly. For example, citizens who report damaged infrastructure or injured individuals during a natural disaster can alert rescue workers to expedite assistance. Some social advocacy organizations use a GIS focused on certain neighborhoods to better serve their communities.

But citizen use can also introduce concerns regarding data privacy and security. People could access the data and use it for harmful purposes, such as tracking an individual’s movements. If government data policies overreach, it could result in breaches to citizens’ data privacy. This is of particular concern to marginalized communities, who could face additional discrimination if GIS data was used to perpetuate harmful stereotypes. Creating trust and buy-in from these communities is key to implementing GIS programs that aim to combat racism and achieve social justice goals.

Data Capture

Data Formats

GIS applications include 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, or 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 a GIS. An example of this kind of information is computer data collected by satellites that show land use, including 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 a 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 a GIS. Maps, however, must first be scanned, or converted to digital format.

The two major types of GIS data formats are called raster and vector data. Raster data are grids of cells or pixels. Raster data are useful for representing GIS data that vary, such as elevation or satellite imagery. Vector data consist of points, lines and polygons. Vector data are useful for representing GIS data with firm borders, such as city boundaries 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.

A 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, a 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. Additionally, some map projections, such as the Mercator map made in 1569 and featured in the Cartographer's Dilemma video, can reflect the biases of the person making them. The Mercator map makes Western Europe appear bigger than it actually is. While mapmakers are working to create more accurate maps, to transfer a curved, three-dimensional shape onto a flat surface inevitably requires stretching some parts and shrinking others. 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

GIS maps have a variety of applications in different fields. Local and federal governments use them to gain more information about communities. Federal governments can use GIS to track the effects of different policies and laws. GIS maps can display what artificial features are near certain natural features, such as which homes and businesses are in areas prone to flooding, which helps local governments prepare for natural disasters.

GIS maps are also useful in science. With GIS technology, researchers can 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.

GIS can produce three-dimensional images, which is helpful for geologists studying earthquake faults. Engineers use GIS technology to support the design, implementation and management of communication networks for cell phones, as well as the infrastructure necessary for internet connectivity.

GIS can be useful in nonscience fields too. 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, as well as where that marketing should be. Museums use GIS to gather information about where their patrons live. They also use GIS to create maps of the museum and its interactive exhibits.

There are many opportunities for governments, businesses and individuals to use GIS to make life easier. But, there are also challenges with privacy and data misuse. Ensuring safety to earn trust and buy-in from users who share their data is key to the future of GIS.

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