AIM. What is-a contour map? 23-

Transcription

1 .. '; AIM 23- What is-a contour map?.,,.,, I. There are many different kinds of maps. The maps we use most often are surface maps. A surface map is a drawing. It shows all or part of the earth's surface. There is one problem with a surface map. It is flat. BUT, the earth's surface is not flat. It has hills and mountains, plains and valleys. And oceans. The different parts of the earth's.surface are at different heights, or elevations. The elevation of the ocean's surface is zero. This is called sea level. The rest of the earth's surface is measured from sea level. So, elevation is measured in feet or meters above (or below) sea level... How can a flat map show elevation? Or changes in elevation? Some maps use color. Others use shading. However, such maps give only a general idea about the surface.. There is a specia'i' kfnc( of map, called a contour (KON toor) map. "Contour" means shape. A: contour map shows the true shape of. the land. It also sh~ws eievations and chariges in elevation. A contour map shows shape and elevation by means of contour lines. A contour line is a Une that connects points that are at the same elevation.... ' -~ Every point on a given contour line is at the same ele.: vation. Several contour lines make up a contour map. The difference in elevation between two neighboring contour lines is called the contour interval of the map. Contour lines can show how much the land slopes. Contour lines that are far apart indicate that the land is fairly flat, or has a gentle slope. Contour lines that are close together show that the land is hilly, or has a steep slope. Hilltops are enclosed by small- contour lines. The exact. elevation of a hilltop is shown by a small triangle beside the true elevation of the hill. For example, A 118 means that the elevation of the peak is 118 feet (or 118 meters). ~ 140

2 .. -., WORKING WITH CONTOUR ~S ) - Look-at the Figures below. 1/-'--'>6 Figure A Figure B Figure A shows an island. Figure B shows a contour map of this island. Answar the questians.below_by studying_the contour map. 1. a) How long is this island? - - b) The long part. runs \ north and south. east and west 2. a) How wide is this island? - -- t. -, hl The wide part runs ncrth!!~d south~ east and west 3. This island starts at sea level. How do you know? (Look only at the contour map.) 4. What is the contour interval of this map?..., a) Which side of the island has the steepest slope? -----,-- -.,----- north, south, east, west b) How do you know? a) Which side of the island has the gentlest slope? ---:----:----:- north. south, east, west b} How do you know? j 7. How. high is the peak of this island?;;..,. -' ,--..,. 141"

3 '-" ) Compare the drawing of the island with the contour map. a) Which one gives more information? , b) Which one is more accurate? --~--- c) Which on~ is more useful? ' ft'l~ei~~-t--> E LAND SCALE 1 c:m ~ 1 km Let's try. another. 1. -By compass direction... ' a) the side of this landform has the steepest slope. b) the side of this -landform has the gentlest slope. 2. The contour interval of this map is -.. meters. 3. The lowest elevation shown is. meters. A 4. Which of these heights could be the exact elevation of the peak? a) 520 meters b) 420 meters c) 475 meters SOMETHING EXTRA You can learn more from a contour map than jusrthe shape and slope of the land. Contour maps also tell you something about streams. And about "dips," or depressions, in the land. STREAMS The head of a stream is the place where it starts. The place where it ends, in a lake or ocean,.is called the mouth. Look at figure D. Can you find a stream? 1. What letter is at..,.,. 142 a) the head of the stream? b) the mouth of the stream?

4 - \\!;. ' ~ 2. When~ cont_?_ll~ lines "cross" a stream, wey a) Eve~yone kriows that water flows -'---7"'7:--:----;-:-;;--- uphlll. downh ill b) In other words, water flow from a elevation to a higher. lower hitlher. lower elevation. 4. At a stream, contour lines se~rn to forra "arrows." Each "a.llrow:" points... a)" b) toward the upstream, downstream head. m ~ ntth of the stream. c) ---.,...---~--the direction of flow. toward. away from t-. w <~ E ~ s FigureD DEPRESSIONS Sometimes a bowl-like dip, or depression, occurs on a fairly flat surface. These are shown by special contour lines catted depression contours. A depression contour is shaded, or hachured, on one side, like this I I 1 1 I 1 II II I The hachures point down into the depression. Depression contours are just like regular contour Hn_~s." They show the shape of the depression. They also show the slope of the sides of the depression. Look at the _depression beside letter B on the map above. 1. )'he elevation at the top of the depression is meters The side of the depression has the steepest slope. J\Urlh, south, east, west Which of these could be the exact elevation at the bottom of the depression ~ a) 40 meters. b) 20 meters c) 10 meters. _ 143

5 COl'vfPLETI~G Com~lcte the se~1tences with the \vurds LH.: lu.v. SENTENCES \ steep contour lines zero (0) contour map g~nlle contour intenr<1l depression contours c!l.!v;.ttlon huchures sea level 1. :\map th_at accurately shows the shape and changing elevations of the land is called ') a ~ The height of a location is called its Contour maps use - to show shape and elevation. 4. All elevations are measured from., 5. The differen.ce in elevation between two neighboring contour lines is called the 6. The number value of sea level is ---~ Dips in a fairly flat surface are shown by------'-' Contour lines that are close together indicate a slope..?.: c 9. The shading marks on a depression contour are calle~ 10. Contour lines that are far apart indicate a slop-e. I'v1ATCHING Match the t»o lists. Write the r.:orrect letter on the line next to each number. L 2. ') '-' head depression contours ele'l.(ation contour interval '<llouth sea level a. height above sea level b, show clips in a flut surfur:o c.. wnere a stream starts ~ -has zero elevation e, -f -G.i-fference between two neighboring contour lines --wtlere a stream ends 14-!: