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# Topographic Maps

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### Topographic Maps

1. 1. Topographic Maps Internet Interactive
2. 2. Below is a Topographic Map Contour line Contour Interval
3. 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. 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. 5. Completed Contour Map with Labeled Contour Lines
6. 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. 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. 8. Any place inside a contour line is HIGHER than the contour line...
9. 9. Anyplace outside the contour line is LOWER than the contour line
10. 10. Contour lines are NEVER left out, so on this map there is no elevation 600’ or less, OR 900’ or higher!
11. 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. 12. Lower contours not shown on the map would appear if we made the map larger...
13. 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. 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. 15. All contour lines eventually make a circle. Sometimes only a part of the circle shows on your map
16. 16. So, is the elevation of contour line D 600’ or 700’? Sometimes you just can’t tell
17. 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. 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. 19. The point of the V always points upstream--toward the higher elevation This river is flowing southwes t
20. 20. The V points upstream-and the river flows the other way!
21. 21. The “V” lets us know the elevation of contour line D…..
22. 22. The “V” points west-upstream, to higher elevation- so the river flows east, to lower elevation, so D must be 600’
23. 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. 24. Relief • Relief: is the difference in elevation between the highest and lowest points in a region
25. 25. No, we’re not done interpreting maps yet...
26. 26. Steepness: the closer together the contour lines, the steeper the slope
27. 27. Depressed? Got yourself into a hole?
28. 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. 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. 30. But don’t get depressed... Get depression contours!
31. 31. A depression contour shows a temporary change in directiona “pothole”. Hachure marks -Everything inside a depression contour is LOWER than the contour
32. 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. 33. The volcano’s topo map Click 
34. 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. 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. 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. 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. 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)