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
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
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)
Be the first to comment