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Topographic Maps

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  • 1. Topographic Maps Internet Interactive
  • 2. Below is a Topographic Map Contour line Contour Interval
  • 3. Contour Lines and Contour Intervals • Contour Line: lines on topographic maps that are of equal elevation. • Contour Interval: distance between two contour lines.
  • 4. Aerial (top) View and Profile (side) View Aerial (top) View Profile (side) view) Click on either picture to see how a topographic map is made to make the contour line.
  • 5. Completed Contour Map with Labeled Contour Lines
  • 6. Calculating the Contour Interval • Find the difference between 2 index contours 2500-1250=1250 or 1250-0=1250 • Then Divide by 5 1250/5=250
  • 7. Spot Elevations: elevations not exactly on a contour line • Point A falls between 0’ and 250’contours • So its elevation is between 1’ and 249’ • (it’s not 0’ or 250’ because those are exactly on the line!) • You can estimate that since A is drawn 1/2 way between contour lines, its elevation is halfway, or 125’
  • 8. Any place inside a contour line is HIGHER than the contour line...
  • 9. Anyplace outside the contour line is LOWER than the contour line
  • 10. Contour lines are NEVER left out, so on this map there is no elevation 600’ or less, OR 900’ or higher!
  • 11. Hills and Valleys • Hills are contour lines in a series of circles where the elevations get higher • Valleys are a series of circles where the elevations get lower OR Where contour lines repeat
  • 12. Lower contours not shown on the map would appear if we made the map larger...
  • 13. • What is the contour Can You Determine interval?______ The Elevation? Click Picture. • What is the Elevation of points. A ___________ B ___________ C ___________ D ___________ E ___________ .G F ___________ G ___________ H ___________
  • 14. Can You Label the Contours? Click on the Picture. • Hints: You know the contour interval is 40’ • Every contour line is a multiple of the contour interval (0,40,80, etc) • You know the elevation 323’. Which 2 multiples of 40 does it fall between? A______________ B______________ C______________ D______________ E______________
  • 15. All contour lines eventually make a circle. Sometimes only a part of the circle shows on your map
  • 16. So, is the elevation of contour line D 600’ or 700’? Sometimes you just can’t tell
  • 17. Sometimes there is a hint. Water always flows downhill. There is a river flowing thru Woodland Valley. If D was a hill (700’)then the river flows east, because water can’t flow uphill
  • 18. The Rule of V’s • Water always flows form higher to lover elevation • contour lines make a “V” shape when they cross rivers
  • 19. The point of the V always points upstream--toward the higher elevation This river is flowing southwes t
  • 20. The V points upstream-and the river flows the other way!
  • 21. The “V” lets us know the elevation of contour line D…..
  • 22. The “V” points west-upstream, to higher elevation- so the river flows east, to lower elevation, so D must be 600’
  • 23. A Quickie Quiz. Click Picture. • In which geographic direction is the river flowing?_________ • What is the elevation of contour lines A_____________ B_____________ C_____________
  • 24. Relief • Relief: is the difference in elevation between the highest and lowest points in a region
  • 25. No, we’re not done interpreting maps yet...
  • 26. Steepness: the closer together the contour lines, the steeper the slope
  • 27. Depressed? Got yourself into a hole?
  • 28. The volcano, with a crater in the middle, rises above a flat plain. C.I.=200’ The highest elevation is at the rim of the crater. The lowest point of the volcano is in the middle of the crater.
  • 29. At the top of the volcano, the contours go crazy... …remember, everything inside the contour is supposed to be higher than the contour!
  • 30. But don’t get depressed... Get depression contours!
  • 31. A depression contour shows a temporary change in directiona “pothole”. Hachure marks -Everything inside a depression contour is LOWER than the contour
  • 32. So, the topographic map of the volcano should look like this: Rule: the first depression contour repeats the elevation of the contour line before it
  • 33. The volcano’s topo map Click 
  • 34. A 3-D Look at Depression Contours C-D is a “regular” valley G-H is a “depression”: a temporary change in direction
  • 35. Interpreting Depression Contours Click on Picture • • • • • • • • • • • Contour A _____ Contour B _____ Contour C _____ Contour D _____ Contour E _____ Contour F _____ Contour G _____ Point q ________ Point r _________ Point w _________ Point y __________
  • 36. Contour Spacing and Steepness • Steep Slope: when contour lines are close together. • Less Steep Slope (gentle/gradual): when contour lines are farther apart. • Contours never touch or cross each other!
  • 37. Steep and Gentle Slopes Profile (side) view of an island Aerial view of island showing contour lines Closer together on the steepest side
  • 38. Gradient • • • • • • • Gradient tells you how steep your route is! It is the difference in elevation (ED) divided by the horizontal distance (HD):  GRADIENT = ED/HD Take a look at this example: The vertical distance (here, the difference in elevation between points 'A' and 'B') = 10,000 feet The horizontal distance from 'A' to 'B' = 5 miles Gradient = vertical distance (elevation difference (ED)) divided by horizontal distance (HD) The GRADIENT is 2000 feet per mile (10,000 feet divided by 5 miles)
  • 39. Other Gradient Examples
  • 40. Gradient Quiz Instructions Click Picture to Take Quiz • • • • • • • • • • • • • • • • • • • GRADIENT QUIZ INSTRUCTIONS In the menu bar under "Select Line", click on "Scale". Click on the "Measure Line" button. A ruler will appear on the map. In the text box next to the question "One inch on map is equal to how many miles?", type in your answer and click on the red check mark. Look in the bottom right 'response text area' for a response to your input. If your answer is not correct, follow the hint and try again. If the response is "Correct!", go to the menu bar again and click on "Line A-C". Then, click on "Measure Line." Next, input an answer to indicate the "Distance on Map" and click on the red check mark. If your answer is not correct, follow the hint and try again. If the response is "Correct!", input an answer to indicate "Actual Distance" and click on the red check mark. If your answer is not correct, follow the hint and try again. If the response is "Correct!", input an answer to indicate "Elevation Difference" and click on the red check mark. If your answer is not correct, follow the hint and try again. If the response is "Correct!", input an answer to indicate "Gradient" and click on the red check mark. If your answer is not correct, follow the hint and try again. If the response is "Correct!", input an answer to indicate which of the illustrated lines has a slope similar to the line whose gradient you have calculated. Then, click on the red check mark. If your answer is not correct, follow the hint and try again. If your answer is correct, go to the menu bar and select the next line to work with. For curved lines, a straightened line and a ruler will appear in the box under the map © 2002 Wayne G. Powell and David J. Leveson
  • 41. Click on Either Picture to Practice Labeling Contours
  • 42. NOW... We’re Done!
  • 43. References • http://academic.brooklyn.cuny.edu/geology/l eveson/core/linksa/maptop.html