Models of the Earth
Chapter 3
Ch03\80017.html
 Geographic North Pole and South Pole - the
points at which Earth’s axis of rotation intersects
Earth’s surface
 Used as reference points for defining direction.
 Equator - halfway between the poles, divides
Earth into the North and South Hemispheres.
 A reference grid that is made up of additional
circles is used to locate places on Earth‘s surface.
parallel - any circle that runs east and
west around Earth and that is parallel to
the equator; a line of latitude
latitude - the angular distance north or
south from the equator; expressed in
degrees
the equator is 0° latitude
The latitude of both the North Pole and
the South Pole is 90°
1° latitude equals about 111 km
Parallels of the Earth
Minutes and Seconds
Minutes - Each degree of latitude consists
of 60 equal parts, called. One minute (°) of
latitude equals 1.85 km
Seconds - each minute is divided into 60
equal parts (°)
 Meridian - any semicircle that runs north and
south around Earth from the geographic North
Pole to the geographic South Pole; establishes
East-west locations
 Longitude - the angular distance east or west
from the prime meridian; expressed in degrees
Distance covered by a degree of longitude
depends on where the degree is measured
Decreases as you move from the equator
toward the poles.
Prime meridian -passes through
Greenwich, England
represents 0° longitude.
International Date Line - The meridian
opposite the prime meridian, halfway around
the world, is labeled 180°
Great circle - any circle that divides the
globe into halves; marks the
circumference of the globe
Any circle formed by two meridians of
longitude that are directly across the globe
from each other
The equator is the only line of latitude that is a
great circle.
The route along a great circle is the shortest
distance between two points on a sphere.
Great circles are commonly used in
navigation, Ex. air and sea routes
magnetic compass - used to find
direction on Earth
Geomagnetic poles - areas on Earth’s
surface just above the poles of the
imaginary magnet
The geomagnetic poles and the
geographic poles are located in different
places.
 Magnetic declination - angle between the
direction of the geographic pole and the direction in
which the compass needle points
In the Northern Hemisphere, magnetic
declination is measured in degrees east or west
of the geographic North Pole.
 Earth’s magnetic field is constantly changing, as is
the magnetic declinations of locations around the
globe
 By using magnetic declination, a person can use a
compass to determine geographic north for any
place on Earth
GPS (global positioning system) another way people can find their location
on Earth
 A satellite navigation system that is
based on a global network of 24
satellites that transmit radio signals to
Earth’s surface
 A receiver held by a person on the
ground receives signals from three
satellites to calculate the latitude,
longitude, and altitude of the receiver on
Earth
Topographic Map Symbols
Symbols are used to show certain features
on topographic maps.
Symbol color indicates the type of feature
 Constructed features - black
Highways - red
Bodies of water - blue,
Forested areas - green.
Contour lines - brown or black
Geologic maps
 Show geologic features
types of rocks found
locations of faults, folds, and other structures
Rock Units on Geologic Maps
 Geologic units are distinguished by color. Units of
similar ages are generally assigned colors in the
same color family, ex. different shades of blue.
 Letters are assigned to each rock unit
symbolizes the age of the rock and the name of
the unit or the type of rock
 Contact line Other markings on geologic maps
 Contacts - indicates places at which two geologic
units meet
faults
depositional contacts
 Geologic maps also indicate the strike and slip of
rock beds.
 Strike - indicates the direction in which the beds
run,
 slip - indicates the angle at which the beds tilt.
Uses of soil maps:
classify
map
describe soils, based on surveys of soils in a
given area.
3 main parts of soil surveys:
text,
maps
tables.
Text - general information about the
geology, topography, and climate of the
area.
Tables - describe the types and volumes
of soils in the area.
Maps - show the approximate locations
and types of the different soils.
Valuable tools for agriculture and land
management.
Used by farmers, agricultural engineers,
and government agencies.
The information in soil maps and soil
surveys helps developers and agencies
identify ways to conserve and use soil and
plan sites for future development.
Maps are useful to every branch of Earth
science.
Maps that are only one useful type of map.
Benefits of using maps:
show the location and flow of water and air
study changes in Earth’s surface over time
show topography and rock and soil types