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A 130 meter-tall hill is the highest place on the landform.Contour maps show the "topography" or shape of the land in two dimensions. Often called "elevation" maps, these maps are easy to read documents that can be easily carried and consulted to find the easiest way to avoid steep inclines and deep valleys when orienteering. Elevation maps can be complex or quite simple, depending on the area covered and the topography of the land. Simple maps may use bands of color to show elevation, but there are only so many colors, so more complex maps use "contours"---lines drawn at specific elevations to show how the land changes. Lines that are drawn close together may indicate a steep hill or cliff and lines that contain parallel "waves" may show a series of ridges. Whatever the topography of an area, it can be accurately shown using contours drawn at regular "intervals" of elevation. -
A plateau 100 metersin elevation seems very steep on its northwest face.Most contour maps use sea level as the zero mark because it is a familiar standard or "convention" (like making direction at the "top" of the map north). The distance between the levels is the interval; say 10 meters, like our example map. In order to keep the map from becoming confusing, a darker line, called an "index" contour, is drawn periodically as a general reference. Maps used by the U.S. military use a standard of one index contour every five lines, so our index contours are drawn at 0, 50 and 100 meters above sea level. There is a "period" of five contour lines between index contours with an interval of 10 meters between each contour line. There appear to be several steep elevations on the map but, since 1 cm equals a mile on the key, making it 6 miles wide and 11 miles long, a more detailed map would be needed to tell. -
Index contours on a barometric pressure map show a windy day in southeast Idaho.Topographers use contouring to record land elevation and forms but other scientists use it, too. One of the more familiar uses for contouring is the barometric map on which meteorologists chart lines connecting locations of identical air pressure measurements. These maps provide scientists with a picture of low and high pressure centers, allowing them to predict weather patterns. Closely spaced contours show where the winds that moved from high-pressure to low-pressure areas are highest as the two masses squeeze together, and the valleys of air pressures along which storms will move. Index contours on weather maps are customarily drawn at a period of 4 millibars (or hectopascals). In addition to the familiar elevation and air pressure maps, social scientists can use contour maps for everything from population movement to political polling. All of these contour maps and charts have conventions that set the interval between contours and the period of the index contours.
