Worked example · Geography · Year 9

Visualising data with maps

DCF: Data and computational thinking → Data and information literacy

What this is

The completed map and the answers, using the same sixteen real USGS records that are printed on the worksheet. Hold a pupil's sheet next to this page to check their plotting: every circle here sits on or beside a dashed plate boundary. The map is drawn into the page itself, so it prints from the browser with no image files and no internet connection.

The symbol rule

Radius for magnitude 6.55 mm
Radius for magnitude 7.59 mm
The rule in one sentenceRadius in millimetres = (magnitude − 6) × 4 + 3, so every extra 0.1 of magnitude adds 0.4 mm.
Why a growing circle?A dot would show only where. The dataset has two variables — position and magnitude — and a proportional symbol shows both at once, so the biggest events stand out without a second map.

Meets criterion 2: one arithmetic rule, stated, so anyone can check that two 7.0 events are drawn the same size.

The finished map

World map of the sixteen largest earthquakes of 2024 Proportional symbol map on a latitude and longitude grid. Circles mark sixteen earthquakes of magnitude 6.5 or more recorded by the United States Geological Survey in 2024. Almost every circle sits on a dashed plate boundary line, with most around the rim of the Pacific Ocean. Earthquakes of magnitude 6.5 and above, 2024 (USGS) -180° -150° -120° -90° -60° -30° 0° 30° 60° 90° 120° 150° 180° -90° -60° -30° 0° 30° 60° 90° Noto Peninsula, Japan M7.5 Atacama, Chile M7.4 Hualien, Taiwan M7.4 Port-Vila, Vanuatu M7.3 Atiquipa, Peru M7.2 Hyuganada Sea, Japan M7.1 Sangay, Philippines M7.1 Cape Mendocino, USA M7.0 Kamchatka, Russia M7.0 Aykol, China M7.0 Pangai, Tonga M6.9 Ambunti, PNG M6.9 Bartolome Maso, Cuba M6.8 Macquarie Island region M6.8 South of Africa M6.6 Port McNeill, Canada M6.5 Key: M6.5 M7.5 — circle radius grows with magnitude plate boundary (sketched) Base map: equirectangular sketch The map wraps at 180°: Tonga (175°W) plots on the far left and Vanuatu (168°E) on the far right, although they are Pacific neighbours.

Meets criteria 1 and 3: all sixteen events are plotted from their coordinates, the westerly longitudes (Tonga at 175°W, Cape Mendocino at 125°W) are on the left-hand side, and the map carries a title, a key that explains the symbol sizes, and the source.

Pattern questions, answered

Question Answer
How many sit around the rim of the Pacific? Thirteen of the sixteen. Working anticlockwise from Japan: Noto Peninsula, Hyuganada Sea, Hualien in Taiwan, Sangay in the Philippines, Ambunti in Papua New Guinea, Port-Vila in Vanuatu, Pangai in Tonga, Macquarie Island, then Kamchatka, Port McNeill in Canada, Cape Mendocino in California, Atiquipa in Peru and Atacama in Chile.
Which are not on the Pacific rim? Three. Aykol in China (41°N, 79°E) is deep inside Asia on the Alpine–Himalayan belt, where the Indian plate is pushing north into Eurasia. Bartolomé Masó in Cuba (20°N, 77°W) is on the boundary between the Caribbean and North American plates. The event listed as "south of Africa" (53°S, 25°E) is in the Southern Ocean on the Southwest Indian Ridge, where two plates are pulling apart.
Two large areas with none at all? Western and central Europe, including the whole of the United Kingdom, has nothing on this map; so does almost all of Africa apart from the ridge event well to the south of it. Northern Asia, eastern South America and Australia's interior are also empty. These are plate interiors, a long way from any boundary.
Magnitude statistics Mean 7.03 (112.5 ÷ 16 = 7.03125). Median 7.0, the average of the 8th and 9th values, which are both 7.0. Mode 7.0, occurring three times (Cape Mendocino, Kamchatka, Aykol). Range 1.0 (7.5 − 6.5).

Meets criteria 4 and 5: the pattern is described with named places and directions, the three exceptions are each explained by a different type of plate boundary, and the statistics are worked from the table with the totals shown.

Which statistic is most useful here?

None of the four says much, and that is the honest answer. The mean, median and mode all land within 0.03 of each other because the dataset was filtered at magnitude 6.5 — every smaller earthquake was excluded before I saw the data, and there were tens of thousands of them. The range of 1.0 is the most informative figure, because it shows how narrow the band I was given actually is. If you want to say anything about typical earthquake size you need the unfiltered catalogue, not this extract.

The strongest point on the sheet: a judgement about what the filter did to the data, rather than treating whatever arrived in the table as the whole picture.

The deep earthquake

The 639.5 km deep earthquake was on 11 July 2024 near Sangay in the southern Philippines, at 6.1°N, 123.2°E. Earthquakes can only happen in rock that is cold and brittle enough to snap, and at 639 km the surrounding mantle is far too hot for that — so the rock that broke must be a slab of cold ocean floor that has been dragged down there. That is subduction: the plate is descending steeply beneath the Philippines and is still breaking as it goes, which is why the deep events line up along the same boundary as the shallow ones rather than appearing at random.

Uses one number from the table to reach a process, which is the step between describing data and explaining it.

Why this response is secure