Topographic Maps
Internet InteractiveMr. Corner
Below is a Topographic Map
Contour line
Contour Interval
Contour Lines and Contour Intervals
• Contour Line: lines on topographic maps that are of equal elevation.
• Contour Interval: difference in elevation between two contour lines.
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.
Completed Contour Map with Labeled Contour Lines
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
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’
Any place inside a contour line is HIGHER than the contour line...
Anyplace outside the contour line is LOWER than the contour line
Contour lines are NEVER left out, so on this map there is no elevation 600’ or less, OR 900’ or higher!
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
Lower contours not shown on the map would appear if we made the
map larger...
Can You Determine The Elevation? Click Picture.
• What is the contour interval?______
• What is the Elevation of points.
A ___________B ___________C ___________D ___________E ___________F ___________G ___________H ___________
.G
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______________
All contour lines eventually make a circle. Sometimes only a part of the
circle shows on your map
So, is the elevation of contour line D 600’ or 700’?
Sometimes you just can’t tell
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
The Rule of V’s
• Water always flows from higher to lower elevation• contour lines make
a “V” shape when they cross rivers
The point of the V always points upstream--toward the higher
elevation
This river is flowing southwest
The V points upstream-and the river flows the other way!
The “V” lets us know the elevation of contour line D…..
The “V” points west--upstream, to higher elevation- so the river flows east, to lower elevation, so D must be 600’
A Quickie Quiz. Click Picture.
• In which geographic direction is the river flowing?_________
• What is the elevation of contour lines
A_____________ B_____________ C_____________
Relief• Relief: is the difference in elevation between
the highest and lowest points in a region
No, we’re not done interpreting maps yet...
Steepness: the closer together the contour lines, the steeper the slope
Depressed? Got yourself into a hole?
The volcano, with a crater in the middle, rises above a flat plain.
The highest elevation is at the rim of the crater. The lowest point of the volcano
is in the middle of the crater.
C.I.=200’
At the top of the volcano, the contours go crazy...
…remember, everything inside the contour is supposed to be higher than the contour!
But don’t get depressed...
Get depression contours!
Hachure marks
A depression contour
shows a temporary change in direction-a “pothole”.
-Everything inside a depression contour is LOWER than the contour
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
The volcano’s topo map
Click
A 3-D Look at Depression Contours
C-D is a “regular” valleyG-H is a “depression”: a temporary change in direction
Interpreting Depression ContoursClick on Picture
• Contour A _____• Contour B _____• Contour C _____• Contour D _____• Contour E _____• Contour F _____• Contour G _____• Point q ________• Point r _________• Point w _________• Point y __________
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!
Steep and Gentle Slopes
Profile (side) view of an island
Aerial view of island showing contour linesCloser together on the steepest side
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)
Other Gradient Examples
Gradient Quiz InstructionsClick Picture to Take Quiz
• GRADIENT QUIZ INSTRUCTIONSIn 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
Click on Either Picture to Practice Labeling Contours
NOW...
We’re Done!
References
• http://academic.brooklyn.cuny.edu/geology/leveson/core/linksa/maptop.html