World Geography

1Thinking Like a Geographer: The Five ThemesGeography asks two linked questions: where things are, and why they are there. To organize that thinking, American geography educators in 1984 published five themes: location, place, human-environment interaction, movement and region. Location describes where something is, either absolutely with coordinates or relatively in relation to other places. Place covers the physical and human features that make somewhere distinctive, while regions group areas that share a characteristic such as climate, language or economy. Human-environment interaction examines how people adapt to and change their surroundings, and movement traces flows of people, goods and ideas. The themes matter because they turn a list of facts into explanations: a city's location on a river helps explain its trade, its growth and even its flood risk. Critics note that the themes are a teaching framework rather than a complete theory, so later standards added skills such as asking questions and analyzing data.
2Latitude, Longitude and Time ZonesLatitude lines run east to west and measure distance north or south of the equator, from 0 degrees to 90 degrees at the poles. Longitude lines run from pole to pole and measure distance east or west of the prime meridian, up to 180 degrees. Finding latitude was relatively easy for sailors, who could measure the height of the Sun or the Pole Star, but longitude required knowing the exact time at a reference point. That problem was solved in the eighteenth century when John Harrison built marine chronometers accurate enough for long voyages. Because Earth turns 15 degrees every hour, the globe can be divided into time zones, and in 1884 delegates at the International Meridian Conference chose Greenwich in London as longitude zero. Time zones also show that geography is political: countries bend zone boundaries and even the International Date Line to suit their trade and national unity.
3Map Projections: Why Every Flat Map DistortsA globe is the only accurate model of Earth's surface, because no flat map can preserve area, shape, distance and direction all at once. In 1827 the mathematician Carl Friedrich Gauss proved that a sphere cannot be flattened without distortion, so mapmakers must choose what to sacrifice. The Mercator projection of 1569 keeps compass directions true, which made it ideal for navigation, but it greatly enlarges areas near the poles, so Greenland looks similar in size to Africa. Equal-area projections such as the Gall–Peters map, promoted by Arno Peters in 1973, keep sizes correct but stretch shapes. Compromise projections like the Robinson and Winkel Tripel balance several distortions for general world maps. Because projections shape how people picture the world, debates about them have also been debates about perspective, with some arguing that enlarging high-latitude regions made Europe and North America seem more important.
4GIS, Remote Sensing and Satellite NavigationModern geographers analyze places with layers of digital data. A geographic information system, or GIS, stores maps as layers such as roads, rivers, population and land use, then lets users overlay them to find patterns, for example which homes lie inside a flood zone. The idea of mapping data to reveal causes is older than computers: in 1854 physician John Snow mapped cholera deaths in London and traced many to a single water pump on Broad Street. Remote sensing gathers information from satellites and aircraft, and the Landsat program has photographed Earth continuously since 1972, making it possible to measure deforestation, urban growth and shrinking glaciers. The Global Positioning System lets receivers calculate position by timing signals from several satellites. These tools raise questions as well as answers: data can be incomplete, and detailed location tracking creates real concerns about privacy.
5Plate Tectonics: The Restless CrustEarth's outer shell is broken into large plates that move a few centimetres a year, roughly as fast as fingernails grow. In 1912 Alfred Wegener proposed continental drift, pointing to matching coastlines, fossils and rocks on different continents, but many scientists rejected him because he could not explain what moved the continents. Evidence from the ocean floor changed that: in the early 1960s Harry Hess proposed seafloor spreading, and magnetic stripes on the seabed confirmed new crust forming at mid-ocean ridges. Where plates pull apart, as in Iceland, new crust forms; where they collide, mountains rise or one plate sinks beneath another in a subduction zone, creating deep trenches and volcanoes; where they slide past each other, earthquakes strike along faults like the San Andreas. Plate tectonics explains why hazards cluster in particular places and why the Pacific is ringed by volcanoes.
6Mountains, Plateaus and PlainsLandforms are the large shapes of Earth's surface, and each tells a story of tectonic forces building land up and erosion wearing it down. The Himalaya began rising when the Indian plate collided with Eurasia, around 50 million years ago, and it is still rising today. Older ranges such as the Appalachians were once comparable in height but have been worn down over hundreds of millions of years. Plateaus are high, relatively flat areas, like the Tibetan Plateau, whose average height exceeds 4,500 metres. Plains, often built from river sediment, are flat lowlands that support farming and dense populations, which is why so many people live on the plains of northern India, eastern China and the American Midwest. Landforms shape human life by steering transport routes, concentrating rainfall on windward slopes and creating barriers that have historically separated languages and states.

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