Topographic Maps8.9C Interpret topographical maps and satellite views to identify land and erosional

features and predict how these shapes may be reshaped by weathering

What are some ways to represent Earth’s surface?

▪ Maps are models that represent Earth’s surface.

▪ They are helpful because they can show large areas of the three dimensional surface on small, flat surfaces.

▪ Different types of maps show different types of information.

▪ Latitude and longitude are used to find places on Earth

▪ All flat maps distort Earth’s surface

Globe:▪ A round map! Here is the same information – flat!

▪ Not very readable is it?

Because the Earth is round and maps are flat, it is impossible to create a map with a perfect scale. Some parts of the map will be too large, while others will be too small. The larger a territory represented by a map, the greater that the distortions in scale will be.

Aerial and Satellite Images

▪ Aerial means taken from airplanes and satellite means from satellites that orbit Earth

▪ Some look like photographs and some are a collection of data that may not be visible (such as infrared that looks at temperatures on earth)

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)

Geological Maps

▪ Geologic maps shows rock types and ages

▪ They also show geological features and fault lines

▪ Colors and letters give information about the rocks, while lines show elevation

Key Features on Maps:

▪ Map title

▪ Compass rose/orientation

▪ Map key or legend

▪ Map scale

▪ Location markers (latitude and longitude)

What’s the difference?

What are the uses of topography in the real world?

Topography has a number of uses including:

▪ Agriculture - Topography is often used in agriculture to determine how soil can be conserved and how water will flow over the land.

▪ Environment - Data from topography can help to conserve the environment. By understanding the contour of the land, scientists can determine how water and wind may cause erosion. They can help to establish conservation areas such as watersheds and wind blocks.

▪ Weather - The topography of the land can have an impact on weather patterns. Meteorologists use information on mountains, valleys, oceans, and lakes to help predict the weather.

▪ Military - Topography is also important to the military. Armies throughout history have used information on elevation, hills, water, and other landforms when planning their military strategy.

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.

Contours and Profiles

You can generate a profile of a landform from the contour lines on a topographic map. But you probably don’t have access to this technology – so what do you do on a trip?

Simple contour map

▪ Imagine you are on vacation with your family in a national park. You have a simple trail map that shows you where to hike. But the map does not tell you anything about what the land looks like. Will you have to cross any rivers or valleys? How far uphill or downhill will you have to hike?

So on your vacation you need - Topographic Maps!

▪ Topography is the shape, or features, of the land.

▪ These features can be natural—such as mountains, plateaus, and plains—or human-made—such as dams and roads.

▪ To show the topography of an area, mapmakers draw a topographic map.

On vacation you would need a topographic map!

▪ People use topographic maps to locate interesting landforms, to find their way through an area, and to determine the direction water flows in an area.

▪ The wiggly lines are called contour lines. They show elevation, slope and relief

Elevation, slope and relief:

▪ Elevation – how high above sea level a place is

▪ Slope – how steep it is. The more gradual a slope, the further apart the contour lines are, the steeper, the closer the lines

▪ Relief – the difference between its high and low points.

▪ For example, subtracting the lowest elevation on a map from the highest, gives you the measure of the area’s relief

Elevation, slope and relief on a map:

A closer look at 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

▪ The contour interval is the same on a map

▪ Get closer together as land gets steeper

▪ Get further apart as land gets flatter

▪ Circles show highest and lowest points

(tops of mountains and bottom of depressions)

Contour Interval

The

distance

that

separates

contour

intervals

The change in elevation from contour line to

contour line is called the contour interval

How do they make topo maps?

▪ There are a number of ways that information is gathered to make topographical maps. They can be divided into two primary methods: direct survey and indirect survey.

▪ Direct survey - A direct survey is when a person on the ground uses surveying equipment, such as levels and clinometers, to directly measure the location and elevation of the land.

▪ Indirect survey - Remote areas may be mapped using indirect methods. These methods include satellite pictures, images taken from planes, radar, and sonar (underwater).

Learning to read topo maps

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

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

▪ More examples and links are posted on my website: Unit 4

Land Features you may see on a Topo Map:

Land Feature - Hill

A small area of high ground. When you are on a hill, the ground slopes down in all directions.

Land Features - Depression

Depression-a low point or hole in the ground, surrounded on all sides by higher ground.

Land Feature - Saddle

▪ Saddle-a dip or low point along the crest of a ridge. A saddle is not necessarily the lower ground between two hilltops; it may be a break along an otherwise level ridge crest.

Land Feature - Cliff

▪ Cliff-a vertical or near-vertical slope. A cliff may be shown on a map by contour lines being close together, touching, or by a ticked "carrying" contour line. The ticks always point toward lower ground.

Grand Canyon – Isis Temple – Can you find the cliffs?

Land Feature - Valley

Valley-reasonably level ground bordered on the sides by higher ground. A valley may or may not contain a stream course. A valley generally has maneuver room within its confines. Contour lines indicating a valley are U- shaped.

Land feature - RidgeRidge-a line of high ground with height variations along its crest. The ridge is not simply a line of hills; all points of the ridge crest are higher than the ground on both sides of the ridge.

PSC 121 Prince George's

Community College

Tracking Flowing Water

▪How does water always flow?

DOWNHILL

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

Tracking Flowing Water (streams)

You can look for elevation changes since water will flow from higher to lower elevations.

Water will always flow down hill so the elevation of the contour lines will decrease in the direction water is flowing.

Here the stream flows toward the northwest.

2100 ft2000 ft

PSC 121 PRINCE GEORGE'S COMMUNITY COLLEGE

Second way to read a stream:The second way to tell is to look at

the pattern of the contour lines.

Because streams will sit in a valley, the land on either side of them will be higher.

As a result the contour lines form a "V" pattern like the one in the red on the map

The point of the "V" points up stream. The open end of the "V" faces downstream. It is the presence of this "V" pattern that was used to recognize stream valleysDownstream Upstream

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, erosion causes steep grades to “soften”. This is shown by the spaces in between contour lines getting wider.

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

How can flowing water shape land?

▪ By weathering and eroding material – Land gets weathered and eroded by flowing water. These, over time, form features such as valleys, cliff and canyons.

▪ Streams carry small pieces of sediment, while larger rivers carry larger particles and major storms can carry even larger pieces, like boulders.

▪ Groundwater below the Earth’s surface form caves and this dissolved material is then eroded and the groundwater flows to new locations.

▪ Deposition by flowing water makes alluvial fans and deltas – which help make flatter landscapes.

▪ Heavy rainfall and floods can cause rivers to rise and bring sediment to higher places

▪ Glaciers are also factor and can carve away entire mountains, or they may form lakes when they recede or melt.

Let’s see what you have learned.

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? How do you figure this out?

1.What is the elevation of point A?

2.What is the elevation of point B?

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

80 m

320 m

880 m

560 m

Map Reading Activity: Topography Practice

Map your hand!

Supplies:

1. Your hand

2. Marker

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