Topographic Mapping8.9C Interpret topographical maps and satellite views to identify land and erosional

features and predict how these shapes may be reshaped by weathering

What is purpose of a topo map?

▪ They show the surface features of an area

▪ Topographic maps add a third dimension to latitude and longitude by showing natural (and cultural) features of the earth’s surface — in particular, elevation.

Texas

▪ Historically, mapmakers used a variety of methods to indicate elevation. To get a quick sense of elevation, we can use color, as in this map.

Using Color vs. Contour Lines

▪ This method of showing elevation wouldn’t help much for a close-up map, though — say, for hiking or roadbuilding. For simplicity, clarity, and accuracy, most topographic maps today use contour lines.

Contour Lines

▪ Contouring is drawing lines on a two-dimensional grid of numbers that connect points of equal value.

▪ In the following grid, for example, The drawn contour lines connect multiples of 10, so we’d say that the contour interval — the space between the lines is 10:

More complicated example:

▪ Here’s a more complicated one — can you see the hills and plains?

Hill

Plains

The contour lines on a topographic map show lines of constant elevation, so it’s easy to see hills, valleys, and plains, and the lines are usually labeled with their elevation.

Contour Lines

▪ Contour Lines are imaginarylines that join points of equal elevation above or below sea level

▪ That’s right – we have even mapped under the ocean!

http://interactive2.usgs.gov

Contour Lines

http://www.4orienteering.com

Equal

elevation

Follow any given line from one side to the other.This continuous line indicates equal elevation.

Rules of Contour Lines

▪ Never cross each other

▪ Connect with themselves

▪ Get closer together as land gets steeper

▪ Get further apart as land gets flatter

Contour Interval

The

distance

that

separates

contour

intervals

The change in elevation from contour line to

contour line is called the contour interval

Connecting Lines practice!

▪ You should have 2 copies of this grid.

▪ Try different contour intervals (5 and 10, say) and see how it affects the finished picture.

▪ What geographical features seem to appear?

▪ Which are more or less prominent depending on the contour interval?

Learning to read topo maps

▪ Learning to use a topographic map is a difficult skill, because it requires students to visualize a three-dimensional surface from a flat piece of paper.

▪ Land Features and other objects are also indicated on a topo map

▪ Topographical map symbols can be found online:

Land Features - Depression

Land Feature - Valley

Land feature - Ridge

Land Feature - Hill

PSC 121 Prince George's

Community College

Tracking Flowing Water

▪How does water always flow?

DOWNHILL

▪How can we tell what direction (N,S,NW,ESE) is downhill?

Tracking Flowing WaterYou can look for

elevation changes since water will flow from higher to lower elevations.

Here the stream flows toward the northwest.

2100 ft2000 ft

PSC 121 PRINCE GEORGE'S COMMUNITY COLLEGE

Tracking Flowing Water

You can look at the contour lines as they cross the stream. They will always point upstream.

Downstream Upstream

PSC 121 PRINCE GEORGE'S COMMUNITY COLLEGE

Tracking Flowing Water

You can also look at where two streams merge. The merge will form a V that points downstream.

Direction of flow

Where erosion may occur▪ a stream would run down the middle or side of the V’s – this is the most

likely place where erosion would occur.

▪ Over time, this could change the landscape

Gradient ▪ The gradient of a mountainside is a measure of its steepness.

Relief

▪ The relief of a contour map is the difference between its highest and lowest points.

▪ Contour interval – 50m

Contours and Profiles

You can generate a profile of a landform from the contour lines on a topographic map.

Simple contour map

Colorado

Notice not only how many lines there are, but how shown on a computer the impression of elevation can be added

Nebraska

This is a satellite topo map. It uses color and shaping to indicate elevation.

Notice Nebraska versus heading west - see all of the mountains?

Put yourself in a map!

Let’s take a walk up a hill!

We’re now at an elevation of 100 meters.

100m

We’re on the peak, but what’s our elevation?

100m

200m

300m

Can we get more precise?

100m

200m

300m

Let’s add contour lines for every 50 meters and see if that

helps.

100m

200m

300m

We know that we are above 350m, but less

than 400m.

50m

150m

250m

350m

100m

200m

300m

Time to go home - Now what’s our elevation?

50m

150m

250m

350m

If you said somewhere between 200m and

250m you are right!

Let’s now look at the same hill, but the way we might see it from an airplane!

Each color change represents a

50 meter increase.

Now, let’s try the same hike! Our

elevation is 0 meters.

Now what is our elevation?

If you said more than 150 meters, but less than

200 meters you’re right!

Let’s go a little higher.

Think you know our elevation

now?

More than 300 meters

But less than 350meters

More on Satellite Views

▪ Satellite views can be used to learn about erosion and how the land has changed

▪ images taken over time can be used for comparison and interpretation of erosional features (ex. after a flood)

Reminder of key terms!

▪ Weathering – is the breaking down of rocks, soil and minerals

▪ Erosion – a process (such as water flow or wind) which removes soil and rock from one location on the Earth's crust, then moves it

▪ Deposition – the location where freshly eroded material gets placed

Let’s see what you know.

800m

1000m

1200m

A

B

C

D

E

F

600m

1. Could the elevation at the peak (B) be 1410 meters?

800m

1000m

1200m

A

B

C

D

E

F

600m

No :The elevation must be under 1400 meters, but over 1300 meters.

2. What is the elevation at (E)?

800m

1000m

1200m

A

B

C

D

E

F

600m

About 400 meters

3. If you walked a straight line from (D) to (C) would you walk over a ridge or down a valley?

800m

1000m

1200m

A

B

C

D

E

F

600m

Down a valley: If the contour lines point up the slope it’s a valley, if they point down the slope it’s a ridge.

4. Just looking at the map, would it be easier to head down from the peak going East, or going North?

800m

1000m

1200m

A

B

C

D

E

F

600m

E

N

S

W

East: When contour lines are close together that means there is a steep slope, the further apart the lines, the more gentle the slope and therefore an easier walk! Go east!

Contour Practice

1. What is the contour interval of the map at left?

2.What is the elevation of point A?

3. What is the elevation of point B?

4.What is the elevation change between A and B?

5.If the horizontal distance between point A and point B is 2.8 km, what is the gradient?

80 m

320 m

880 m

560 m

200 m/km

Make a Mountain!

Supplies:

1. Ruler2. Playdoh3. String 4. Wax paper

Follow instructions on the page to build and map your own mountain!

Close to Home

▪ Local maps

▪ http://www.topozone.com/states/Texas.asp?county=Bexar

▪ http://www.trails.com/topo.aspx?lat=30.50639&lon=-98.81861&s=50&name=Enchanted%20Rock

▪ Topo Map - http://www.youtube.com/watch?v=EqyfJMgFL-U