What is a map?

A Map is a two or three-dimensional

model or representation of the Earth’s

surface.

2-Dimensional

map

What is a “Map Projection”?

Planar Projection

Projection

A Projection is a mathematical means of

transferring information from the Earth’s

three-dimensional curved surface to a two-

dimensional map.

Types of Map Projections

All map projections are “flawed” by

distortions that are created during

“projection”. Different map

projections have been developed to

reduce this distortion to different

areas of the map for different

purposes.

Cylindrical Projections

Notice the effect that different types of projections

have on the shape of meridians (lines of longitude)

and parallels (lines of latitude).

Mercator Projection (Cylindrical Projection)

• Great Distortion of area and shape at high latitudes.

• True shapes and distances within 15 Degrees of the Equator.

Map Distortions

Greenland

Mercator map sizeTrue size of

Greenland

In this image, Scandanavia (high lat.) is

Larger than India (equatorial).

Planar or Polar Projections

• Has little distortion towards poles or the plane you are looking at.

• Distortion increases as you get further from the poles or the plane

you are viewing.

Conical Projections

•When several conic projections are put together

shapes and sizes of land masses are almost the same

as a globe.

Robinson Projection

• Makes things “look right,” it comprises a few different types to try

to balance out distortions

•Better balance of size and shape of high latitudes, and low

distortion within 45 degrees of the Equator.

• Used by National Geographic for world maps since 1988, and

replacing Mercator in schools.

Robinson Projection

• Can still see some distortion at poles

Latitude and Longitude

Where am I? Early Greeks and Chinese attempted

to create a grid system to help them answer this

question. But it was not until the Middle Ages that

the latitude/longitude system was developed.

Latitude and Longitude

Cartographers (mapmakers) have established a set of

vertical and horizontal grid lines that cover the globe

called:

Parallels- Lines of Latitude (horizontal)

Meridians- Lines of Longitude (Perpendicular)

Because the Earth is a sphere, each line represents a 1

degree slice of the 360 degrees in a the sphere.

Lines of Latitude

Equator

Parallels dissect

the Globe like a

a tomato is cut.

Latitude Line “Rules”

•Run East to West

•Measure distance in degrees from the

Equator

•Each line forms a circle around the

Earth that is vertically equidistant from

the equator.

• Numbered from 0 to 90 Degrees

(0 being the equator, and 90 being the

poles)

Lines of Longitude

Prime Meridian

Longitude Line “Rules”

•Run North to South

•Measure distance in degrees from the Prime-

Meridian

•Form half-circles that are equidistant from each

other at the Equator, but converge at the poles.

• 0 Degrees Longitude is at Greenwich, England

(established in 1883); 180 Degrees is in the

Pacific, and is called the International Date Line

(divides the Globe between two days).

Time Zones

The Earth takes 24 hours to rotate once on its axis.

Therefore, the Earth has been divided into 24 Time

Zones.

Time Zones are a geophysical world globe division of

15o each, starting at Greenwich, England, created to

help people know what time it is now in another part

of the world (see page 76 in your text for a good Time

Zone tool).

International Date Line

0 degrees Longitude

0

-1 +1

-11

+10

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The Earth can be divided into

vertical and horizontal halves called

Hemispheres.

The Equator-Divides Northern

and Southern Hemisphere

Equator

The Prime Meridian-Divides

Eastern from Western Hemisphere.

Prime

Meridian

The Degree is the basic unit of

Latitude and Longitude

A general location on the globe would be

shown as 45 N.

A more precise location on the globe

would be 45 15’ 35” N.

How “big” is a Degree?

Each degree in Latitude and Longitude is

approximately 69 miles “wide” at the equator.

Each degree can be divided into 60 subdivisions called

minutes (1.15 miles in “width”). 45’

Each minute can be divided into 60 subdivisions called

seconds (.019 miles, or 100 feet!). 35”

So, your location on the globe can be very precisely

identified, and would look like this: 97 35’ 42” N.

Every spot on Earth has an

address that is determined by

referencing, in degrees, minutes

and seconds, the latitude and

longitude of that location.

YOU ARE HERE!

Map Scale

Map Scale expresses the relationship between

the distance on a map and the true,

corresponding distance of the same area of the

Earth’s surface.

Mapmakers can't draw maps the same size as

the area they represent; the maps would be too

big. So they draw features smaller than they

actually are.

A map scale is usually given as a fraction

(1/10000) or a ratio (1:10000)

USGS maps contain scales that have the same

units on both sides of the ratio.

Fractional scale

The larger the number on the

right, the greater the amount of

land that the map represents.

1:100000 scale 1:24000 scale

Bar Scale

A bar scale is just a line drawn on a map

of known ground length. There are

usually distances marks along the

line. Bar scales allow for quick visual

estimation of distance.

Pay attention to where the zero point on

the bar actually is when you measure

with a bar scale!

Notice that 0 is here!

Magnetic Declination

Because Magnetic North and Geographic-

North are only the same in very few places,

the direction in which the compass needle

points is called Magnetic North, and the

angle between magnetic north and true north

is called Magnetic Declination.

Magnetic North

True North

Declination or Degrees Off Course

Error Off Target after Walking 10 Miles

1° 920 feet (280meters)

5° 4,600 feet (1,402 meters)

10° 9,170 feet (2,795 meters)

Effect of Magnetic Declination

Topographic Maps

A Topographic Map is the

representation, normally on a flat

surface,of part of the Earth’s

surface, drawn to scale.

Topographic maps show distance

relationships and elevation.

Topography actually means,

“the shape, elevation and slope

of the land”.

One of the main features of

topographic maps are contour

lines.

How do we know where to put

the lines when we make a map???

Well, we could do it this way!!

We could start with an island, and

increase the level of the ocean the

amount of our contour interval, an

marking the shore line as we raise

the water level.

10 feet above normal sea-level

Notice that the shape of the island

changes. Why?

20 feet above normal sea-level

30 feet above normal sea-level

Now, drain the water, and we

have our topographic map!

But, how do they do it

for real??

Survey Tools

“Fish Finder”

Contour Lines are Imaginary lines that

join points of equal elevation on the

land above or below sea level.

All points on this line have an elevation

of 250 feet above sea level, for example.

There are several different

kinds of contour lines.

Index Contour (darker, has elevation)

Intermediate Contour (lighter; does not have

elevation identified)

Intermediate Contour

Depression Contour Lines

Perp. Lines point

downhill, into the

depression

Lip of

depression is

highest point

220240

260

280

**Edge of

depression is

between

240-260.

Contour Lines make it possible to

determine the shape of the land without

looking at the actual spot.

Ridge

Valley

Topographic maps also include

symbols that represent such features

as woods, houses and roads.

WoodsStreams

Roads

House

Contour IntervalContour Interval

Total Distance between Index Contours =

Number of Spaces between Index Contours =

Slope

Steep SlopeGentle Slope

Elevation increase between two identified

points/distance between two horizontal

points.

Line A Distance

= .5 miles

Elevation Change =

Slope =

Topographic

Profiles

Topographic Profiles

Stream Direction

Determining stream direction of flow helps

the map reader interpret elevations of

intermediate contour lines above or below an

Index Contour.

Notice V shape of

canyon slopes

V’s point uphill. Therefore, line

A must be less than 900, and

line B must be more than 900

A

B

Vertical Exaggeration