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 twodimensional 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 size

True 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 Parallels dissect the Globe like a a tomato is cut.

Equator

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 PrimeMeridian •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).

0 degrees Longitude

-11

International Date Line +10

0 -1

+1

I N T E R N A T I O N A l

D A T E L I N e

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 GeographicNorth 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.

True North Magnetic North

Effect of Magnetic Declination 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)

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

280 260

**Edge of depression is between 240-260.

240

220

Ridge Valley

Contour Lines make it possible to determine the shape of the land without looking at the actual spot.

House Streams

Woods

Roads

Topographic maps also include symbols that represent such features as woods, houses and roads.

Contour Interval Contour Interval

Total Distance between Index Contours = Number of Spaces between Index Contours =

Slope

Gentle Slope

Steep 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