AP® Human Geography · Unit 1 · Topic 1.2
GIS, Satellite Navigation, and Remote Sensing
GIS stacks digital map layers so you can find places that meet several conditions at once, GPS uses satellite trilateration to pin a location, and remote sensing collects data about the Earth from satellites or aircraft instead of from people on the ground.
A geographic information system, or GIS, stores spatial data in separate layers: one layer for roads, one for zoning, one for flood zones, one for schools. Each layer is georeferenced, meaning every feature is tied to real coordinates, so layers line up perfectly when stacked. The power is in overlay: a planner can ask the system to show only the parcels where all four layers agree, something that is nearly impossible to eyeball on paper maps. This is why GIS is the tool of choice whenever a question involves several conditions at once rather than a single map.
GPS, the satellite navigation system that gives GIS its real-time location data, works through trilateration. Each satellite broadcasts the exact time its signal was sent. A receiver on the ground, like a phone, measures how long each signal took to arrive and converts that travel time into a distance from that satellite. One distance narrows your location to a sphere around the satellite; four satellites give four overlapping spheres, and the single point where they all intersect is your location. More satellites in view generally means a tighter, more accurate fix.
Remote sensing is the third piece: gathering data about the Earth's surface from a distance, usually satellites or aircraft, without sending anyone there to measure it directly. It replaces or supplements ground reports with continuous imagery, so a drought map can update daily using soil moisture and vegetation readings instead of waiting on scattered field surveys. GIS, GPS, and remote sensing work as a system, satellites feed location and imagery data in, GIS organizes and overlays it, and the result is a map that updates and answers complex questions fast.
Key terms
- GIS (Geographic Information System)
- Software that stores spatial data in layers and lets users overlay and query them together.
- Trilateration
- Finding a location by converting signal travel time from multiple satellites into distances and finding where they overlap.
- Remote sensing
- Collecting data about the Earth's surface from satellites or aircraft rather than from ground visits.
- Georeferenced
- Tied to real-world coordinates so a data layer lines up accurately with other layers or maps.
- Overlay
- Stacking multiple GIS data layers to find locations where several conditions are all true at once.
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