Below is a Topographic Map
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
Calculating the Contour Interval
• Find the difference
between 2 index
• Then Divide by 5
Spot Elevations: elevations not exactly
on a contour line
• Point A falls between 0’ and
• So its elevation is between 1’
• (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
• Valleys are a series of
circles where the
elevations get lower
Where contour lines
Lower contours not shown on the
map would appear if we made the
Can You Determine
The Elevation? Click Picture.
• What is the contour
• What is the Elevation
Can You Label the
Contours? Click on
• 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?
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
water can’t flow
The Rule of V’s
• Water always flows
from higher to
• contour lines make
a “V” shape when
they cross rivers
The point of the V always
points upstream--toward the higher
The V points upstream-and the river
flows the other way!
The “V” lets us know the elevation
of contour line D…..
flows east, to
D must be
A Quickie Quiz. Click Picture.
• In which geographic
direction is the river
• What is the elevation
of contour lines
• Relief: is the difference in elevation between
the highest and lowest points in a region
A 3-D Look at Depression Contours
C-D is a “regular” valley
G-H is a “depression”: a temporary change in direction
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 __________
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 lines
Closer together on the steepest side
• 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
• The GRADIENT is 2000 feet per mile (10,000 feet divided by 5 miles)