The maps that we use online work because of geographic information systems (GIS).

A GIS is a kind of computer system. It captures, stores and displays data about locations on Earth.

It can use and compare any information about a location. The location can be expressed in many different ways. One example is an address. Another is latitude and longitude. These are imaginary lines that appear on common maps of Earth. Lines of latitude run east-to-west. Lines of longitude run north-to-south. These lines are used to find any place on Earth.

GIS helps us find out how different bits of information relate to each other. It tells us about the landscape and people around us.

GIS is a helpful tool. But there are some problems with it too. These maps are expensive to set up. People who make the maps need special training. The system can be hard to learn. The maps can also be incorrect if they use old data.

There are also worries about privacy. People give maps data to use. This can be very helpful. For example, people can report damage during a storm. This helps rescue efforts reach damaged buildings or hurt people faster. Organizations that help people can also use these maps. But GIS can also be used in bad ways. Someone could get into the data and follow someone else’s movements. This would harm their privacy. Someone could also use data to further mistreat people who face racism and other types of discrimination. This is why it's so important for people running GIS to have proper protections for the data.

Data Capture

Data Formats

GIS data comes in many forms.

One example is cartographic data. This includes objects you might find on maps. Examples are rivers, roads, hills and valleys.

Interpreting photographs is a big part of GIS. This involves photos that are taken from above. These images are then carefully studied.

Digital data can also be entered into GIS. For example, satellites collect computer data from space. This can show how land is used, such as the location of farms, towns and forests.

Finally, GIS data can also be collected to compare populations of people. For example, imagine you had a list of everyone's age in your state. With GIS data, you could compare the ages of people in your city to those in other cities. It would be laid out on a single map.

Spatial Relationships

GIS technology can be used to show how two spaces are related. For example, GIS could show how close farms are to water. It can also show patterns of how land is used, like where parks and neighborhoods are located.

It can also show networks of lines on a map. A line on a map might stand for a road, river or highway. With GIS layers, however, that road might show the boundary of a public park next to the river.

GIS must make information from many different maps and sources fit together on the same scale. A scale is the relationship between the distance on a map and the actual distance on Earth.

Earth is curved, like a globe. It is not flat, like a paper map or a screen. A projection is a way of taking information from Earth's curved surface and showing it as something flat. Different maps have different projections. But you cannot put a curved, three-dimensional shape onto a flat surface without stretching some parts. For example, the map in the Cartographer's Dilemma video is stretched. It shows a projection called the Mercator map. In this map, Western Europe looks bigger than it is in real life. The European mapmaker Mercator made it that way because many Europeans at the time thought Europe was one of the most important parts of the world. Today, mapmakers are trying to make maps more exact, but they will always be a little stretched.

GIS puts together data from maps that were made using different projections. It combines them so all the information can be displayed using one shared projection.

GIS Maps

GIS maps are used in many different jobs. Governments use them to get information about communities. The maps can help politicians make new laws and see how those laws work in certain places. GIS maps can also help governments prepare for big storms.

Maps are helpful in science. Researchers can study changes over time with GIS technology. They can use pictures taken by satellites to study how ice sheets have moved or disappeared in the North Pole. GIS maps also help people study earthquakes. 

There are uses for GIS outside of science and government. They help people set up cell phone networks and internet access. Businesses can use GIS to help them figure out where to open a new store. Museums use maps to create their exhibits and to figure out where people are coming from when they visit.

GIS maps can make people’s lives easier. But there are also problems with privacy that can happen. People who make maps need to earn trust from the people who use them. Then GIS maps can help everyone.