Topographic MapsTopographic Maps

Lesson ObjectivesLesson Objectives

Define a topographic map and state Define a topographic map and state its uses.its uses.

Describe how contour lines show the Describe how contour lines show the elevations, shape, and slope of the elevations, shape, and slope of the land.land.

Identify the meanings of some Identify the meanings of some symbols and colors used on symbols and colors used on topographic maps.topographic maps.

What is a topographic map?What is a topographic map?

A topographic map, also known as a A topographic map, also known as a contour map, is a map that shows the contour map, is a map that shows the shape of the land using contour line. shape of the land using contour line.

It is a map that shows and elevation field, It is a map that shows and elevation field, meaning how high and low the ground is meaning how high and low the ground is in relation to sea level.in relation to sea level.

What are contour lines?What are contour lines?

Contour lines are lines that connect points that Contour lines are lines that connect points that are of the same elevation.are of the same elevation.

They show the exact elevation, the shape of the They show the exact elevation, the shape of the land, and the steepness of the land’s slope.land, and the steepness of the land’s slope.

Contour lines never touch or cross.Contour lines never touch or cross.

What is a benchmark?What is a benchmark?

A benchmark is a point where exact A benchmark is a point where exact elevation is known and is marked elevation is known and is marked with a brass or aluminum plate. It is with a brass or aluminum plate. It is marked BM on the map with the marked BM on the map with the elevation numbers given in feet.elevation numbers given in feet.

Benchmarks are useful to help Benchmarks are useful to help determine contour lines.determine contour lines.

Other Topographic TermsOther Topographic Terms

Map scale – compares distances on Map scale – compares distances on the map with distances on earth.the map with distances on earth.

Legend – explains symbols used on Legend – explains symbols used on the map.the map.

Index contours – contour lines that Index contours – contour lines that are labeled to help you find the are labeled to help you find the contour interval.contour interval.

What is a contour interval?What is a contour interval?

A contour interval is the difference in A contour interval is the difference in elevation between two contour lines elevation between two contour lines that are side by side.that are side by side.

Remember that a contour interval is Remember that a contour interval is not the distance between the two not the distance between the two lines – to get the distance you need lines – to get the distance you need to use the map scale.to use the map scale.

What if my contour lines are close What if my contour lines are close together?together?

If the contour lines are close If the contour lines are close together, then that indicates that together, then that indicates that area has a steep slope.area has a steep slope.

What if my contour lines are far What if my contour lines are far apart?apart?

If the contour lines are far apart, If the contour lines are far apart, then that indicates the land has a then that indicates the land has a gentle slope (low slope).gentle slope (low slope).

What do the dark colored contour What do the dark colored contour lines mean?lines mean?

The dark colored contour lines The dark colored contour lines represent every fifth contour line to represent every fifth contour line to make it easier to read the map.make it easier to read the map.

What do depressions in the map What do depressions in the map look like?look like?

A depression, such as the inside of a dead A depression, such as the inside of a dead volcano, is represented by Hachure lines.volcano, is represented by Hachure lines.

Hachure lines are regular contour lines Hachure lines are regular contour lines with small segments sticking out from it.with small segments sticking out from it.

The first hachure line is at the same The first hachure line is at the same elevation as the contour line before it.elevation as the contour line before it.

More on Contour LinesMore on Contour Lines

Contour lines form V’s that point Contour lines form V’s that point upstream when they cross a stream. upstream when they cross a stream.

It is important to remember that they It is important to remember that they point in the opposite direction as the point in the opposite direction as the flow of water.flow of water.

What do the colors on the What do the colors on the topographic map represent?topographic map represent?

Blue lines/shapes - represent water Blue lines/shapes - represent water features, such as streams and lakes.features, such as streams and lakes.

Brown – contour linesBrown – contour lines Black – Roads, buildings, railroads, Black – Roads, buildings, railroads,

other man made objects.other man made objects. Green – Woodland areasGreen – Woodland areas Red - HighwaysRed - Highways

Now that I know what a topographic Now that I know what a topographic map is, how do I read it?map is, how do I read it?

First determine the contour interval First determine the contour interval (the distance between each contour (the distance between each contour line)line)

Then determine the map scale Then determine the map scale (usually at the bottom of the map)(usually at the bottom of the map)

Identify any hills or depressionsIdentify any hills or depressions Use the legend to identify man made Use the legend to identify man made

features.features.

Reading a topographic map cont.Reading a topographic map cont.

Look for areas where the contour Look for areas where the contour lines are close together – they lines are close together – they indicate a steep area.indicate a steep area.

Look for areas where the contour Look for areas where the contour lines are spread apart – they indicate lines are spread apart – they indicate a gentle slope.a gentle slope.

Review QuestionsReview Questions

How are contour lines drawn on How are contour lines drawn on maps?maps?

How does a contour map show How does a contour map show whether a slope is gentle or steep?whether a slope is gentle or steep?

What is a benchmark?What is a benchmark? How is a benchmark shown on a How is a benchmark shown on a

map?map? How is distance measured on a How is distance measured on a

contour map?contour map?

THANK YOU FOR ATTENTIONTHANK YOU FOR ATTENTION