Topographic Maps

Topographic Maps

A topographic map of part of Ithaca

Topographic Maps

• Maps of an elevation field

• Show elevation by contour lines

• Also show other natural and

man-made features by using

symbols

HOW TO READ TOPOGRAPHIC MAPS

1. Contour lines – lines the connect points of equal elevation

• Contour Lines close together – • Contour Lines far apart –

Steep slopeGentle slope

2. Contour Interval The contour interval on this map is 20?

What do you think is a contour interval?

Contour IntervalChange in elevation in between two

consecutive contour lines

Usually listed in key or legend

If you are at sea level, your elevation is 0.

The contour line for the coastline is 0.

3. Index Contour Line

• The Index Contour lines on the map below are the 700 and 800 lines

Why do you think they are darker?

Index Contour Lines

• Every 4th or 5th line that is thicker or bolder

• Line is labeled with the elevation

• Helps to read the map

Index contour lines are placed every 50 units on this map

What is the spacing of Index Contours on this map?

What is the contour interval?

4. Hills

• How is a hill depicted on a topographic map?

Hills

• Closed contours in a circle or elliptical (oval) shape

• “Bulls eye”

5. Depressions

• The opposite of a hill is a depression which is a low point in the ground. They are represented by hachure lines.

Describe what a hachure line looks like.

Feathered line or a line with hash marks

5. Hachured Lines

• Does the elevation go up or down when you see the hachured lines?

• The first depression line is going to the ________ elevation as the closest contour line

down

same

6. Benchmark - EXACT Elevation

Indicated by a BM or X on a topographic map

• What is the exact elevation of the benchmark on this map?

2919 feet

7. Streams always flow Downhill – from higher elevation to lower elevation

Can a stream flow northward? Yes

What direction is this stream flowing?

South

N

Describe what the contour lines look like when they are crossing a stream?

Contour lines point in the opposite direction the stream is flowing!

N

Streams always flow in the opposite direction the V or U is pointing.

8. Maximum Elevation of a HillSteps 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

• How is the highest possible elevation?

Highest contour line = 40

Pretend one more so that would be 50

Subtract 1

50 – 1 =

Maximum elevation of hill is 49

9. Minimum Elevation of a Depression

Steps to follow:

1. Count down the contour lines using the contour interval.

2. Pretend that there is one more contour line at the bottom of the depression (imaginary line).

3. add 1

Map Scales

• The relationship between distance as measured on a map and the actual distance on Earth’s surface

Types of Map Scales

a. Verbal Scale – 1 inch = 20 miles

b. Bar Scale

One Mile

Types of Map Scales

c. Ratio Scale -

One of any unit on this map represents 24,000 of the same unit on Earth’ s surface.

Ex, one inch would equal 24,000 inches on the Earth

• 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