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

ProjectionA 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.

Map Distortions

Greenland Mercator map size

True size of Greenland

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 are horizontal lines on a map that show latitude, positions north and south of the equator.

Meridians- Lines of Longitude are vertical lines on a map that show longitude, positions east and west of the prime meridian.

Because the Earth is a sphere, each line represents a 1 degree slice of the 360 degrees in a the sphere.

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

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).

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?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” W.

Every spot on Earth has an address that is determined by

referencing, in degrees, minutes and seconds, the latitude and

longitude of that location.

Map ScaleMap ScaleMap 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.

Bar ScaleBar 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!

Map Orientation• Orientation is determined by Cardinal directions of North, South, East and West.• A compass is usually to determine the cardinal directions on the ground.• A compass does not normally point to true north. Only in a few places does True North and MagneticNorth line up with each other. The direction in which the compass needle points is referred to as Magnetic North, and the angle between magneticnorth and true (geographical) north direction is called 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”.

Different symbols and colors are used to indicate

various features on topographic maps, including

bodies of water and human-made structures.

Topographic Maps

A topographic map of Portland, Maine shows various physical features of the area.

Topographic maps also include symbols that represent such features

as woods, houses and roads.

WoodsStreams

Roads

House

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???

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??

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

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

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