Contour Lines

Contour lines are lines drawn on a map that connect points of equal elevation. If you walk along a contour line you neither gain or lose elevation.   Picture walking along a beach exactly where the water meets the land (ignoring tides and waves for this example). The water surface marks an elevation we call sea level, or zero.

As you walk along the shore your elevation will remain the same, you will be following a contour line. If you stray from the shoreline and start walking into the ocean, the elevation of the ground (in this case the seafloor) is below sea level.  If you walk in the other direction and walk up the beach your elevation will be above sea level. 

Above Sea Level Sea Level Below Sea Level

Why are contour lines useful? Contour lines are useful because they allow us to show the shape of the land surface (topography) on a map.  Hiking Camping Construction engineering

http://maps.nrcan.gc.ca/topo101/elevation_e.php

Sea Level

Rising Water Imagine someone flew to this island and ran around the shoreline marking sea level with brown paint, labeling it 0’. Each morning she awoke to discover the water level had risen another 500’ and each morning she ran around the island marking the levels with her brown paint and labeling them accordingly

Contour Lines Remarkably, on the eighth day she rose and discovered that just as mysteriously as the water had risen, it had fallen back down to it’s original level. Now all the lines marking the different levels could be seen. Isolines are lines that connect points of equal value on a map. When working with contour (topographic) maps these isolines are referred to as contour lines. What value do these contour lines represent? Eleveation or height. Contour lines join points of equal elevation. As you see on the picture in the left hand corner there is a notation saying contour interval (C.I.) = 500’. What do you think this means? (Answer: the contour interval is the difference in value between two contour lines) Why do you think we need to establish contour intervals for our contour lines?

What is this? This is an aerial view of the island that *name* drew the contour lines on.

CONTOUR MAP This is a Contour Map. This is a two dimensional model of the islands surface. By labeling the contour lines we can see what the elevations are at various points.

10 characteristics of contour lines 1. Contour lines are continuous. 2. Contour lines do not cross each other- but there are 2 exceptions 3. A series of V-shape indicates a valley and the V’s point to higher elevation.

characteristics of contour lines cont. 4. A series U shape indicates a ridge. The U shapes will point to lower elevation. 5. Evenly spaced lines indicate an area of uniform slope. 6. A series of closed contours with increasing elevation indicates a hill and a series of closed contours with decreasing elevation indicates a depression.

characteristics of contour lines cont. 7. Closed contours may be identified with a +, hill, or -, depression. 8. Closed contours may include hachure marks. Hachure marks are short lines perpendicular to the contour line. They point to lower elevation. 9. The distance between contour lines indicates the steepness of the slope. The greater the distance between two contours the less the slope. The opposite is also true.

characteristics of contour lines cont. 10. A different type of line should be used for contours of major elevations. For example at 100, 50 and 10 foot intervals. Common practice is to identify the major elevations lines, or every fifth line, with a bolder, wider, line.

1. Contours are Continuous Some contour lines may complete full circles (connect) but others will not. In this case, they will start at a boundary line and end at a boundary line. Contours must either close or extend from boundary to boundary.

2. Contour lines do not cross Two exceptions: They will meet at a vertical cliff They will overlap at a cave or overhang. When contour lines overlap, the lower elevation contour should be dashed for the duration of the overlap.

3. Valleys and higher elevation A valley is shown by a series of V-shapes where the V’s point to the higher elevation.

4. U shapes and ridge A series of U shapes indicates a ridge. The U shapes will point to lower elevation.

5. Contour Spacing Evenly spaced contours indicate an area of the same slope. Unevenly spaced contours indicates an area with variable slope.

6 & 7 Hills and Depressions A series of closed contours with increasing elevation indicates a hill. Hills may be identified with a “+” with the elevations

6 & 7 Hills and Depressions--cont. A series of closed contours with decreasing elevation indicates a depression. Depressions may be identified with a “-”.

8. Hachures Hachures are short lines which are perpendicular to the contour line. Used to indicate a hill or a depression. Not used on modern maps.

9. Contour Spacing Contours spaced wider apart indicate lower slope. Contours spaced close together indicate a higher slope.

9. Contour Spacing-Intervals Another decision that must be made is the contour interval. The “best” interval depends on the use of the data.

10. Contour line The thicker contour is Called the index line. http://www.doe.mass.edu/mcas/images/db/05s08q37.gif

How do you make a contour map? Contour lines never cross Contour lines never end- unless they go off the map There must be equal intervals between contour lines When contour lines are closer together, the slope is steeper When the contour lines are spaces farther apart, the land is less steep

Contour Map

Play-doh worksheet