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Home›World geography

Continents and oceans

Seven continents, five oceans, the highest and deepest places, the longest rivers and the driest deserts, then the grid of latitude and longitude, time zones and the maps that flatten the globe. Every number comes from the CIA World Factbook, NOAA, USGS or National Geographic.

Progress

About this course

Why is Greenland an island and Australia a continent? Both are surrounded by sea. The usual answer is size and convention: Australia, at about 7.7 million square kilometres, is more than three times larger than Greenland, at about 2.2 million, and geographers long ago agreed to call the largest such landmass a continent. Greenland is the largest island, and New Guinea, at about 786,000 square kilometres, is second. Questions like this are where the course begins. Every number comes from the CIA World Factbook, NOAA, USGS or National Geographic.

The seven units move from the biggest shapes to the finest lines. After the continents and the five oceans, one unit takes the highest and deepest places: the Challenger Deep lies 10,924 metres below the surface, 2,075 metres farther down than Everest rises. Great rivers and deserts shows the Nile and the Amazon differing by about 214 kilometres, so how you measure decides which comes first. Latitude and longitude come next, then time zones, where Kiribati straddles the 180 degree meridian and its Line Islands now keep UTC+14. The final unit is map projections, since on a Mercator map Greenland looks about as big as Africa, which is about 14 times larger. The 3D globe lets you click any country to see its continent, find countries by name, and turn to the poles to watch the meridians meet.

Longitude was much harder than latitude for sailors. The answer was a clock: the Earth turns 15 degrees an hour, so a ship's clock set to Greenwich time that reads 2 p.m. at local noon puts the ship 30 degrees west.

Before you start

This course is a good starting point for geography, so nothing has to come first. The time zones unit divides 360 degrees by 24 hours, and several questions compare areas in millions of square kilometres, so being comfortable with large numbers and simple division is all you need.

When you finish

You will be able to list the seven continents and the five oceans in order of size, give the height of Everest and the depth of the Challenger Deep, and say why the Nile and the Amazon trade places as the longest river. You can read latitude and longitude, work out time differences at 15 degrees an hour, and explain why Greenland looks too big on a Mercator map.

  1. 1The seven continentsAsia alone covers about 44.6 million square kilometres, almost six times the area of Australia.
  2. 2The five oceansThe Pacific Ocean covers about 168.7 million square kilometres, more than all the land on Earth put together.
  3. 3The highest and deepest placesThe floor of the Challenger Deep lies 10,924 metres below the sea surface, 2,075 metres farther down than Everest rises up.
  4. 4Great rivers and desertsThe Nile and the Amazon differ in length by about 214 kilometres, and how you measure a river decides which one comes first.
  5. 5Latitude and longitudeOne degree of latitude covers about 111 kilometres anywhere on Earth, but a degree of longitude shrinks to nothing at the poles.
  6. 6Time zonesThe Earth turns 360 degrees in 24 hours, so every 15 degrees of longitude moves noon by one hour.
  7. 7Map projectionsOn a Mercator map Greenland looks about as big as Africa, yet Africa is about 14 times larger.

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Sources for this course (15)
  • CIA World Factbook, final edition (cia.gov/the-world-factbook, retired in 2026; read from the archived copy and the factbook.json mirror of the same text): World entry (Geographic overview, Area, Area - rankings, Elevation, Major rivers, Major lakes, Major watersheds, Climate)
  • Antarctica, the five ocean entries (Area, Elevation, Country name etymology)
  • Russia, China, United States, France, Kiribati, India, Nepal, South Korea and Greenland (Area, Capital time difference and time zone notes)
  • NOAA National Ocean Service: How many oceans are there? (oceanservice.noaa.gov/facts/howmanyoceans.html)
  • What is latitude? (facts/latitude.html)
  • What is longitude? (facts/longitude.html)
  • What is the international date line? (facts/international-date-line.html)
  • USGS: Deserts: Geology and Resources, What is a desert? (pubs.usgs.gov/gip/deserts/what/)
  • FAQ How much distance does a degree, minute, and second cover on your maps? (usgs.gov/faqs)
  • Map Projections poster (pubs.usgs.gov/gip/70047422)
  • National Geographic Education: Not all Deserts are Sandy (education.nationalgeographic.org/resource/deserts)
  • Selecting a Map Projection (resource/selecting-map-projection)
  • Investigating Map Projections (resource/investigating-map-projections)
  • National Geographic, "There's a new ocean now" (nationalgeographic.com, 8 June 2021)
  • International Meridian Conference vote: greenwichmeantime.com/articles/history/conference and University of Hawaii, Exploring Our Fluid Earth. Kiribati 1995 date change: timeanddate.com/time/dateline.html.

Checked: 2026-10-17