Chapter 3
Models of the Earth
Section 1: Finding Locations on Earth
The Earth is divided into hemispheres, North & South and East & West. These
hemispheres are then further divided into other areas.
Latitude
Distance in degrees North or South of the equator
Uses parallels as lines East and West of the equator
A parallel is any line that completely circles the Earth and is parallel to the equator.
They are the same distance throughout the Earth’s Surface
Lat. of the equator is Oo
North Pole is 90o N.
South Pole is 90o S.
1o of Lat is 1/360 of circumference 40,000
360
1o of Lat is approx 111km
1o = 60 minutes (60’) = 111km
1 minute of lat = 1.85km
1 second of lat = 0.031
Longitude
Distance in degrees East or West of the Prime Meridian
Measured in meridians
A meridian is a circle that runs north and south
Furthest you can go is 180o away (circle is 360o)
Divided into degrees and minutes (1o = 60’)
Closer the lines get together the further from the equator you are
At the equator 1o is about as long as 1o of latitude (111km), but the distance gets
smaller the closer you are to the poles. The equator is a meridian.
Riverhead Long Island, New York is approx: 40o 55’ 1”N 72o 39’ 43”W
Greenport Long Island, New York is approx: 41o 6” 12”N 72o 21’3”W
Disney World, Florida is approx: 28o 24’ 41” N 81o 31’ 58” W
Great Circles
Great circles are straight lines that go all the way around the center of the earth. The
equator is the only line of latitude that is a great circle. Meridians of longitude that
cross over the north and south poles are also great circles. For every location on a
great circle, it's antipodal location is also on the circle. Other than the equator itself,
any great circle crosses the equator at two antipodal locations, 180° apart. Other than
the equator and meridians of longitude that run due north and south, any great circle
reaches its maximum latitudes at two locations that are 90° of longitude east and west
of the two locations where the great circle crosses the equator.
Antipode – the location 180° on the other side of the world. Example 40 north’s
antipode would be 40 south, and so on.
Prime Meridian -
the longitudinal line that passes through Greenwich, England
Oo Long (also passes through Spain, Algeria, Ghana, Burkina and Mali) It dates back to
October 1884. At the behest of the President of the United States of America 41 delegates from 25 nations met in
Washington, DC, USA for the International Meridian Conference
Finding Direction
Magnetic declination
Is the difference of the angle between true north and magnetic north. This number will
change as you move around the earth. This is because a compass will point toward the
magnetic north (also called the geomagnetic north) and we use polar north for direction
without a compass
Global Positioning System
GPS
Tells position (latitude and longitude), speed and time (based on the
global network)
If used by the military can be accurate to the centimeter
Found in most cars and can also be hand held with an accuracy of 10 to
15 meters.
Very accurate because it 3 satellites for triangulation for accuracy
Earth Observing System
EOS
Established in 1999
Unlike maps that show images, this system maps the changes in air from
the ground to the atmosphere in all areas, even the water, it shows the
exchange of carbon, water and energy.
http://www-airs.jpl.nasa.gov/Technology/HistoricalContext/
Section 2 Mapping Earth's Surface
Cartography- the science of making maps
Cartographer – Mapmakers
Uses data collected from various sources.
Map - a way of looking at the earth; shows earth as flat - it is
not therefore there is distortion
One Type of such a map is:
Remote Sensing – using satellites or airplanes to gather
information without being there
Map projection
A map is flat so it is hard to show depth, they accomplish this by using a
technique called map projection.
Map Projection: A way of showing the curved earth as flat; there is still
some distortion, either in distance or direction or both.
The three most popular map projections used today:
Cylindrical or Mercator projection
It shows the whole world except extreme Polar Regions;
shows true direction; polar region is exaggerated! Uses
straight lines; looks like a grid. Used for sea navigation.
Azimuthal or Gnomonic projection
It shows that a straight line between two points is the shortest distance; direction
and distance are not perfect. Looks like wedges - from the poles down. Used for air
travel. Distorts both direction and distance.
Conic or polyconic projection
Are a cone of a small area covered by these maps make them nearly
correct in all aspects. Used by the U.S.G.S. (United States Geologic
Survey). Lines of lat. and long have slight curves.
When more than one conic map is used it is called Polyconic.
Reading Maps
Direction on a Map
You first need to figure out what compass direction you are looking at.
Most maps drawn by the United States Geological Survey (USGS) has
North on top of the page. However, if north is not up on top they need a
way of showing you direction by using a compass rose.
Compass Rose - usually a picture showing where North, East, South,
West are located. Some maps may use only a single arrow to do this.
Some use an elaborate pointed symbol.
Symbols
A legend is a list of symbols and their meanings. They include urban, city or other
areas.
Symbols are standardized colors:
Scales
Maps most also include a way to measure distances. They accomplish by using a scale.
Graphic - is printed and looks like a ruler
Fractional using ratios
1/100 - map size is one-hundredth real size 1: 100
Verbal - statement
1 Centimeter represents 50 kilometers
Isograms
Is a line of equal value. All points on the line are the same value. This can be used for
many different types of maps used in different sciences.
Section 3 Topographic Maps
Advantages of Topographic Maps
•Uses natural features and constructed features to represent an area. They are made by
using both aerial photos and survey points.
•They show elevation.
•They are very detailed maps about the surface of an area, it will cover all areas, size,
shape, elevation.
•Uses isolines to show outlines of land forms.
Benchmark - exact elevation on a brass or Al Plate
Done by U.S.G.S. to the nearest foot
Labeled BM on maps
Elevation of Topographic Maps
Relief - the ability of a map to show land forms
1. Elevation - mountains, hills – High Points
2. Depressions - kettle holes, valleys – Low Points
Contour lines:
• Give exact elevation (depression) above sea level (below) and
show general shape of the land
•Everywhere on the contour line is the same exact elevation
•Can show areas of valleys, ridges, mountains, etc.
Contour interval
Is the difference in elevation between two consecutive contour lines.
Depression contours
1.
Gives depression measurements
2.
Drawn with lines on inside of contour intervals
Landforms on Topographic Maps
Any point on a contour line is exactly the elevation of the contour line
Any point between contour lines is an estimate in between the two contour lines
No contour lines - (few) very little change in elevation
A lot of contour lines - very steep change in elevation
Closed circles show tops of hills
A ridge is an oval contour line
Rivers - Contour lines always point upstream from where the river is flowing
Topographic Map Symbols
Contour lines are brown
Roads, buildings, railroads & works built by man are black
Water is blue
Woodland areas is green
Highways are red
Developed areas are pink
ProfileIt is to make a side view of the area on a topographic map. It
is also a cross sectional view of the area. This is important to
be able to see what the features of the area are.
Gradient =
Change in elevation (Ft)
(Slope) distance
(miles)
Other types of Maps
Geologic - Shows the soils in and distribution of geologic features
Soil Maps - show information about area. Used by Natural Recourse Conservation
Services (NRCS)