1 topographic maps show the shape of the earth’s surface

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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

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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 v-shape 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 one mile on the map

Represents parts of one mile, ex: one tenth of a mile

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 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 This is what you might you might expect the expect the “profile” or “profile” or cross section cross section view of line view of line AB to look AB to look like! like! Notice how Notice how the line dips the line dips below 250m below 250m where it where it crosses Long crosses Long CreekCreek

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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 of water flow.

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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