Images to Depict Urban Development

In addition to GIS, geographers use other technological components to explore and understand the world. Satellite technology provides access to positional data. GPS (global positioning system) or GNSS (Global Navigation Satellite System) receivers rely on a network of satellites that determine our position on the surface of the Earth and our elevation or vertical position.

GPS satellites and ground stations, installed and maintained by the United States, provide horizontal and vertical positional data. The GNSS includes the U.S. GPS and those from other countries, such as the European Union (Galileo), Russia (GLONASS), and China (BeiDou). Figure 1.4 illustrates the orbits of these satellites relative to Earth, the International Space Station (ISS), and the Hubble Space Telescope. The ISS and Hubble Space Telescope are in low Earth orbit (LEO).

Satellites, aircraft, and uncrewed aerial vehicles (UAVs) capture remotely sensed imagery, a valuable source of geospatial data. This imagery includes data on Earth's land cover, elevation, magnetic field, weather, and climate, among other phenomena. For example, the U.S. National Aeronautics and Space Administration/U.S. Geological Survey (NASA/USGS) Landsat program has been capturing satellite imagery of the Earth's surface since 1972. Geographers and other scientists use this imagery, which is free to the public, to track changes in land cover over time.

For example, Figure 1.5 illustrates the increase in urban development in Casablanca, Morocco, from 2005 to 2018.