USGS Learning Web :: Lesson Plans :: Exploring Maps

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Lesson 1: Location

How do we know where we are?

For the most part we sense our surroundings visually. We may see canyons, rivers, sand dunes, mountain peaks, schools, roads, or other landmarks: we understand our surroundings as a collection of visible features.

We also think of places in terms of other places. For example, you know where you live relative to friends' houses, school, and so forth. From downtown to the boondocks, distances and directions to other significant places for part of our understanding of places in the world. In a larger way, we have also come to understand the relationship between our surroundings and the Sun, Moon, and stars by carefully observing the changing sky.

A great number of devices have been invented to measure places. The first tools, invented thousands of years ago, were simple gadgets: the level, the sight, the measuring chain. Mathematics developed geometry to describe shapes and relationships of objects in space. The magnetic compass, the sextant, the telescope, the theodolite, the planetable, and the marine chronometer, used in combination with mathematics, have greatly increased mapping accuracy.

Developments in mapping continue today with advances in computer hardware and software, lasers, and satellites, which carry remote sensing devices around the earth and to distant places in the solar system.

Technological innovation and the advancement of science have gone hand in hand. The development of agriculture eventually led to land ownership, which led to surveying and taxes.

In the third century B.C., the Greek astronomer and mathematician Eratosthenes used observations of shadows and distances to calculate the circumference of the Earth. His calculation, about 25,000 miles, was accurate to within 500 miles.

Observations of stars, planets, and other objects in the sky, meanwhile, were being recorded with great accuracy (as shown, for example, on the 1193 Suchow Planisphere), changing people's understanding of the relationship of the Earth and the heavens.

Local measurements of distances and direction provided detailed information about small areas; little by little, this information was compiled on less detailed maps of larger areas (for example, the 1109 Beatus map, the 1452 Mappa Mundi, and the 1502 Cantino Planisphere), presenting broader views of the Earth as it was thought to be. Many of these old maps, however, also include conjecture and decoration, without distinguishing between the known and the unknown.

As mapping entered the Renaissance, European navigators used the magnetic compass in navigation, developing portolan charts. In the late 1600's, surveyors improved accuracy by using Galileo's telescope and a technique called triangulation. In this process, the location of a new point is determined by measuring a distance between two known points and measuring angles from each end of this line to the new point.

Although solar observations were useful for measuring distances north and south (latitude), accurate measurement east and west (longitude) was not possible until 1765, when the marine chronometer was introduced. This was the first precise portable clock unaffected by the rocking motion of ships.

Beginning in the 19th century, photography and the aerial viewpoint revolutionized mapping. By the 1920's, aerial photographs were found to be excellent mapping tools, especially when viewed through the stereoscope, revealing a three-dimensional image. Photogrammetry and remote sensing from satellites and airplanes have extended the mapper's view to distant planets and beyond.

Additional Activities

Invite a surveyor to demonstrate today's tools to the class.
Select two quotations from the Explorer Section that seem especially pertinent to this activity sheet, and write an essay that discusses the ideas of both writers.