Topographic Maps September, 2011

MAP A model of Earth’s surface. Best model is a globe (no distortion). Flat maps are made but they usually contain some distortion (like flattening an orange peel). The smaller the area drawn (or of curvature) the less the distortion.

FIELDS Any region of space that has some measurable value of a specific quantity at a specific location. Temperature, pressure, wind speed, humidity, elevation, etc. Most change with time (dynamic).

Representation of Fields ISOLINE – a line that connects equal values in a field. Types include . . . Isotherms – connect equal temperatures. Isobars – connect equal pressures. Contour Lines – connect equal elevations.

GRADIENT The rate at which a field changes from one place to another (over a distance).

GRADIENT The closer the isolines, the steeper or greater the gradient. 10 miles 2 miles Gradient = 10°F/10 miles = 1°F/mile Gradient = 10°F/2 miles = 5°F/mile The closer the isolines, the steeper or greater the gradient. The further apart the isolines, the gentler or lesser the gradient.

TOPOGRAPHIC MAPS A two-dimensional model of Earth’s surface that shows elevation at various locations. Also called Contour Maps.

Rules For Reading Topographic Maps Topographic maps have lines on the surface connecting points of equal elevation (contour lines).

Rules For Reading Topographic Maps The difference in elevation between any two adjacent contour lines in the contour interval. 10,200 10,100 10,300 CONTOUR INTERVAL: 10,400 10,600 100 meters 10,700

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Rules For Reading Topographic Maps Hill tops are indicated by closed loops.

What is the highest contour line? _________________ 10,700 What is the highest elevation of the hill? ____________________________________________ Must be above 10,700 but below 10,800

Rules For Reading Topographic Maps A bench mark is a location whose exact elevation is known and is noted on a brass aluminum plate.

Rules For Reading Topographic Maps Topographic maps are usually oriented so that North is at the top. Many maps have map scales at the bottom to show linear distance.

Rules For Reading Topographic Maps Depressions are usually indicated by closed loops with hachured lines inside. The first line of a depression contour has the same value as the contour line just crossed before the depression was come upon.

Rules For Reading Topographic Maps Contour lines bend to form a “V” in a valley with the point of the “V” pointing uphill. A stream always flows out of the “V” if it crosses a contour line. Cold Creek

Rules For Reading Topographic Maps The spacing of contour lines can show gradient. The closer the contour lines, the steeper the gradient. The further apart the contour lines, the gentler the gradient. B to C = Steep Gradient A to B = Lesser Gradient C to D = Least Gradient

GRADIENT = 22°F 28°F – 22°F 3 meters = 2°F/meter 28°F

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PROFILES A side view of a section of a contour map showing the slopes in the region. 3900

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