What is a map?
A Map is a two or three-dimensional
model or representation of the Earth’s
surface.
2-Dimensional
map
Types of Maps:
(just a few that we may be using)
• Political Maps
– Shows borders of states, countries, etc., may have lat and
long. Could be road maps, may show buildings, etc.
• Topographic Maps
– Use contour lines to show different physical landscape
features and their elevations (like mountains, rivers,
canyons, etc.)
• Climate Maps
– Shows information about the climate of an area. May use
contour lines or isobars to show pressure, temperatures,
fronts, rainfall, etc.
• Resource Maps
– Shows the specific type of economic activity or natural
resources present in an area through the use of different
symbols or colors
What is a “Map Projection”?
Planar Projection
Projection
A Projection is a mathematical means of
transferring information from the Earth’s threedimensional 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 Example)
Great Distortion of area and shape at high latitudes.
• True shapes and distances, where it is most
accurate is within 15° of the Equator.
•
Map Distortions
Greenland
Mercator map size
True size of
Greenland
Planar or Polar Projections
• Has little distortion, so most accurate, 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, but most
accurate 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 – see the dots
are larger near the polar region.
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 are the same distance apart.
•Numbered from 0 to 90 Degrees north
or south of equator.
(0 being the equator, and 90 being the
poles)
Lines of Longitude
Prime Meridian
International Date Line
I
N
T
E
R
N
A
T
I
O
N
A
L
D
A
T
E
L
I
N
E
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).
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 (.019 miles,
or 100 feet!). 35”
So, your location on the globe can be very precisely
identified, and would look like this: 7 35’42”N, 77 10’30”W
Let’s Practice… (remember latitude goes first)
71° 00’ 45”
5°
5°
5°
What is the location of the following points?
A = 5°59’45”N, 71°00’45”W
B = 5°59’09”N, 71°01’00”W
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.
Cartographers, 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.
Magnetic Declination
Because Magnetic North and GeographicNorth (which is the north pole) 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
So here in VA our magnetic declination is almost 10° W. (so there is almost 10°
difference between true north and magnetic north where we are located).
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)
So here in VA, if we did not take into account for magnetic
declination, then we may be close to 9,000 feet away from the
destination we are aiming for.
Topographic maps show distance
relationships and elevation.
Topography actually means, “the
shape, elevation and slope of the
land”.
We use survey tools and
satellites to make contour
lines and topographic maps.
Survey Tools
Satellites
There are several different kinds of
contour lines.
Index Contour (darker, has elevation written)
Intermediate Contour (lighter; does not always
have elevation identified)
Depression Contour Lines
Perp. Lines point downhill, into the
depression
Lip of
depression is
highest point
280
260
220
Contours will also come into play with other types of
maps we look at – like for weather.
These contours show
temperature.
These contours (isobars)
show pressure.
Contours will also come into play with
other types of maps we look at – like for
weather.
• Contour lines that show pressure on a weather
map are called isobars.
• The “H” is area
of high pressure
and the “L” is
area of low
pressure.
• Areas of low
pressure usually
have storms.