Topographic Maps
Show the shape of the
Earth’s surface.
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A topographic map of part of Ithaca
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 List three situations when you
might use a topographic map instead
of a road map.
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Contour Lines
• As contour lines become further apart…
– The gradient decreases – not steep
• As contour lines become more closely
spaced…
– The gradient increases - steep
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Contour Lines
• Closed contours appearing on a map as
ellipses or circles represent hills or
knolls
• Closed contours with hachures
represent depressions
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What is the pattern of the contour lines
around a simple hill?
Concentric
circles
getting
smaller hill
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Identify the features marked at A and B
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Hachure contour lines (lines
with tick marks) show
depressions – the first hachure
is equal to the last contour line
passed
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WHAT DOES THIS PROFILE
SHOW?
VOLCANO
NOTICE HACHURE
DEPRESSION LINES IN
CENTER SHOWING
VOLCANIC VENT 10
Contour Lines
• Contour lines don’t
cross each other
– Although at a vertical
cliff they may be on
top of one another
• Where contour lines
cross streams and
rivers they have a vshape and the v
points upstream
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Contour Interval
• The elevation change between
contour lines is the Contour Interval
• The vertical distance that separates
each contour line on a topographic
map
• The contour interval is stated on
each map
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Contour Interval
 What is the contour interval on this map?
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Index Contour Lines
• These are heavy lines spaced at
predetermined elevations on a
topographic map
• Are usually labeled with a number
somewhere along the line
 What might you use index contours
for?
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Index contour lines
are placed every 50
units on this map
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 What is the spacing
of Index Contours on
this map?
 What is the contour
interval?
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Map Symbols
• The United States
Geological Survey
(USGS) uses the
same map symbols
on every map.
• Most USGS maps
do not have a key –
you need to provide
your own!
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Colors
on Topographic Maps
– Blue stands for water
– Green stands for forested areas or woods
• Green dots lined up in rows show an
orchard
– Black is human-made structures
– Pink stands for high population areas
– White stands for non-wooded areas
– Red represents for highways
– Brown indicates contour lines
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Map Scale
• The relationship between distance as
measured on a map and the actual distance
on Earth’s surface
– One of any unit on this map represents 24,000 of
the same unit on Earth’ s surface
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• Maps often give you more than one way to
measure distance
Represents parts of
one mile, ex: one tenth
of a mile
Represents one
mile on the map
One kilometer
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Known Elevations
– Places of known elevation are shown with the
abbreviation “BM”
• BM stands for benchmark
• An “X” and elevation number might appear
with the BM
• BM, X and the elevation are written in
BLACK
• Benchmarks are set in concrete and checked
periodically by the USGS
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This is what a Benchmark looks like.
Extra Credit: bring in a “rubbing” from a local benchmark.
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Maximum Elevation of a Hill
Steps to follow:
1. Count up the contour lines using the
contour interval.
2. Pretend that there is one more contour
line at the top of the hill (imaginary line).
3. Subtract 1
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So, if we were to look at a profile
view of line AB on our
topographic map, what might we
expect to see? Predictions?
Time to FIND OUT!
Step 2
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Make the X-axis exactly as long as line AB.
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Next, decide what the HIGHEST and LOWEST elevation values
are that line AB crosses on your topographic map and create a
scale. You may wish to increase your scale by the contour interval
on the map to make things easier. In this case, we are going up by
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10’s, because our contour interval on the map is 10 meters.
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Hold your scrap paper page up to the profile.
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Transfer the tick marks directly onto the profile.
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This is what
you might
expect the
“profile” or
cross section
view of line
AB to look
like!
Notice how
the line dips
below 250m
where it
crosses Long
Creek
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Does it make sense? SURE! There is a creek flowing through this
region. Think about where it would flow on your profile. We also
recognize the V shaped contour lines that indicate the direction 44of
water flow.
The contour lines point up the page (orange),
but Long Creek flows down the page.
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Contour lines point upstream.
Stream flows from high elevation to low
elevation. So a stream flows in the oppostite
direction the contours point.
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CONTOUR LINES BEND WHEN CROSS STREAMS
UPSIDE DOWN V’S POINT UPSTREAM
STREAMS FLOW DOWN
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