GPS — timing signals from four satellites
GPS (Global Positioning System) is a network of orbiting satellites, each broadcasting its own position and the exact time the signal was sent. A receiver in a phone, car or handheld picks up at least four of them, times how long each signal took and converts that into a distance from each satellite. Combining those distances is trilateration, and it fixes latitude, longitude and altitude. GPS outputs a position only: no map, no route, no directions.
Satnav — GPS position plus maps plus routing
Satnav is built on top of GPS. It combines the current GPS position, digital map data on the device (roads, junctions, speed limits, landmarks) and route-planning software that routes to the destination entered and gives turn-by-turn directions, spoken or on-screen. As position updates keep arriving it recalculates automatically after a wrong turn and shows an estimated arrival time; many also pull live traffic data over a mobile network.
GIS — layers of location-linked data
A GIS (Geographic Information System) captures, stores and analyses data tied to a geographic location, drawing it as layers over a base map — roads, population density, flood-risk zones, customer addresses. Layers can be switched on and off or combined, so patterns a plain table of numbers hides become visible. That analysis drives real decisions: town planning, resource allocation, delivery route optimisation and emergency-service dispatch.
Drawn from real examiner reports.
GPS is positioning, satnav is navigation
A frequent wrong answer says GPS "gives you directions". It does not: GPS only calculates a position — a set of coordinates — by timing satellite signals, and knows nothing of roads, destinations or routes. Satnav is the layer above it, adding map data and route-planning software. The test: a phone can use GPS to geotag a photo while doing no navigation at all.
GIS is not a map with a dot on it
Because a GIS also displays a map, candidates describe it just as they would satnav — "it shows where you are and how to get there". That misses what defines GIS: it holds several layers of location-linked data and lets them be combined and analysed, for example overlaying customer addresses onto a flood-risk zone. Name the layering and a decision it supports.
Satellite TV is one-way; satphone two-way
Both are satellite links, so candidates blur them. Satellite television is a one-way broadcast: one transmitter sends the same signal to many dishes at once. A satellite phone is two-way: an individual handset both sends and receives its own signal, more like a mobile call than a broadcast. Equipment differs too: a fixed dish versus a portable handset.
Vague terms score nothing here
"Satellite technology" is too vague to earn a mark. State which one the question is about — GPS (positioning), satnav (navigation), GIS (data-layer analysis), satellite television (broadcast) or satellite phone (two-way voice/data) — each has its own characteristics, uses, advantages and disadvantages. Echoing a stem term back earns nothing either.
Satnav is not infallible
A satnav fix is not always right. The receiver needs a clear line of sight, so tunnels, tall buildings and tree cover cause signal loss; position can be out by several metres, because timing and atmospheric errors feed the trilateration; and map data goes out of date, missing a new road or closure. Hence over-reliance: following an obviously wrong instruction.
Satellite links need a clear sky path
Satellite links are not immune to conditions. Satellite television suffers rain fade — heavy rain disrupts the picture, because the signal travels far further through the atmosphere than a cable does. A satellite phone needs a clear view of the sky: tree cover, a building or a tent blocks it. GIS has its own version: an out-of-date layer misleads.
Give a reason, not a bare claim
"Satnav is useful" scores nothing. Explain and describe answers need a because: "satnav recalculates the route automatically after a wrong turn, because it keeps receiving updated GPS position data". Every advantage and every disadvantage carries its own reason.
An advantage needs a comparative
A benefit is one-sided; an advantage compares. "A satellite phone gets a signal" is a benefit. "It gets a signal where a mobile phone has no mast coverage" is an advantage. On advantage, disadvantage, compare or discuss questions, put a comparative in every point.
Compare on the same feature
Never split a comparison into a satellite-television list and a separate satellite-phone list — it prevents a real comparison and caps the marks. Take one feature at a time, answered on both sides: direction of communication, users served, equipment needed, typical use.
Anchor uses to a no-coverage scenario
Satellite phones and television are chosen precisely where no ground infrastructure reaches — no mobile mast, no cable. Say that. "It works everywhere" names no reason and scores nothing; "a ship at sea is far from any mast, so only a satellite link reaches it" does.
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