Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of...

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Reading Contour Lines “The Basics”

Transcript of Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of...

Page 1: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Reading Contour Lines

“The Basics”

Page 2: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you neither gain or lose elevation.

Page 3: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Picture walking along a beach exactly where the water meets the land. 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 stray the other direction and walk up the beach your elevation will be above sea level (see diagram at right).  

Page 4: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

• The contour line represented by the shoreline separates areas that have elevations above sea level from those that have elevations below sea level. 

• We refer to contour lines in terms of their elevation above or below sea level. In this example the shoreline would be the zero contour line ( it could be 0 ft., 0 m, or something else depending on the units we were using for elevation).  

Page 5: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

The two diagrams below illustrate the same island.

From the profile it is clear that the topography of the island is more complicated than what is indicated by a map with one contour line.

Page 6: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

• If we flood the island with 10 feet of water, we can see that the island appears to be smaller.

• Only the land with an elevation greater than 10 ft is above the water line.

New contour line is 10 ft.

Page 7: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

What will happen to the island as we continue to add water 10 ft at a time?

Notice the island gets smaller and smaller.

Page 8: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

• Taken all together the contour lines supply us with much information on the topography of the island. 

• With practice we can picture topography by looking at the map even without the cross profile.

Page 9: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Reading Elevations• The map below is an enlargement of the map of the

previous island.  Each of the letters from A to E represent locations for which we wish to determine elevation.  Use the map and determine (or estimate) the elevation of each of the 5 points.

Page 10: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Contour Interval

• The contour interval is constant for each map.

• It will be noted on the margin of the map.

• You can also determine the contour interval by looking at how many contour lines are between labeled contours.

Page 11: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Using Index ContoursWhat is the contour interval?

20 meters

Page 12: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

What are the elevations of points A-D?

Page 13: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Depression Contours

• Shows decreasing elevations

• What is the lowest possible elevation? 31 meters

Page 14: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

Relief to Contours

Page 15: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.

River Contours

Contour lines that cross river beds bend in the opposite direction of river flow

They Point upstream

Page 16: Reading Contour Lines “The Basics”. Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you.