TOPOGRAPHIC MAPS

What do topographic maps DO?!?

In contrast to most maps, a topographic map shows the shape of the Earth’s surface by using contour

lines.Contour Line - a special type of

isoline that connects points of equal elevation (distance above sea level)

on a topographic map

The United States government prints topographic maps for every square INCH of our country.

It is conducted by the USGS (US Geological Survey) They have been doing this since 1897!! They update individual maps in a timely manner. There are 54,000 individual maps to cover the entire

United States. They are called “quadrangles” - probably because they

are quadrilaterals!

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SEA LEVEL

RISING WATER

Contour Lines

CONTOUR MAP

Steepness

ALWAYS the first things that you must determine when looking at a topographic

map are the contour intervalcontour interval and the map scalemap scale!

WHY?!You just might be asked to

calculate the gradient! DUH!!

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Map Map ScaleScale

• Ratio of the distance on the map to the distance on the ground

1. Graphic:

Map ScaleMap Scale

2.Verbal:

“1 inch equals 10 miles”

Map scaleMap scale

3.Representative fraction or ratio:

1:24,000

• Units don’t matter

SPECIFICS!!1) The top of a hill may not be exactly the same as a

contour line. Therefore, you may need to say what the “highest possible” elevation is:

The elevation at point “D” is higher than 160 feet above sea level, because it is inside the 160 ft contour line.

So what is the HIGHEST it can possibly be?

.E

What is the highest possible elevation for point E?!?

Hachured Lines A “hachured line is a “hairy line” which shows a hole

in the ground. DEPRESSION - a hole in the ground There are special rules that apply in this situation

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The value of the first hachured line REPEATS the value of the last

“normal” line!

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A 3-D View of a Depression

2) Finding the LOWEST possible elevation at the bottom of a depression:

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What is the lowest possible elevation at the bottom of this depression?

61 feet!!

RIVERS

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To figure out the direction a river is flowing, you look at the “bends” in the contour lines that cross over the river.

The “blip” points UPstream (where the watercomes from).

The water flows DOWNstream!

Towards which compass direction is the Green River flowing?

It is flowing towards

the NW!

What about these?

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