1. Models of the Earth
Chapter 3.1

2. Finding Locations on Earth
While the Earth’s shape is not a sphere is very close to the shape.
This makes it very hard for us to pinpoint locations without having reference points.
The North and South Geographic Poles are used for mapping reference and establishing directions.

3. Finding Locations on Earth
Halfway between the North and South Poles is the equator.
Based from these reference points we have created an entire system of intersecting circles to locate places on Earth.

4. Latitude
Parallels are circles (lines) that run east and west around the world parallel to the equator. They describe positions north and south of the equator.
The angular distance north or south of the equator is called latitude.

5. Latitude Latitude is measured in degrees (symbol = º).
There are 90 degrees between the equator and either pole.
There are a total of 360 degrees of latitude lines to make a full circle
360 º = 40,000km around the Earth.
Parallels of latitude north of the equator are labeled with an N, and parallels of latitude south of the equator are labeled with an S.

6. Latitude
Latitude is broken in to measurements of degree, minutes, and seconds.
One degree of latitude = 60 minutes (Symbol = ‘)
One degree = 111 km
One minute = 60 seconds (Symbol = “)
One minutes = 1.85km
Washing D.C. is located at 38º53’51”N.
How many km does 1” equal?
(0.031km).

7. Longitude
A meridian is a semicircle running from the north pole to the south pole.
Meridians make up all of the north/south lines on the earth.
They are used to establish an East/West location.
The Prime Meridian passes through Greenwich, England and is 0 º.
The degrees of meridians begin at 0 º and go to 180 º East or West.

8. Longitude
Longitude is the angular distance, measured in degrees, east or west of the prime meridian.
It is also measured in degrees, minutes, and seconds.
We know that Washington D.C. is located 38 º 53’51”N on the parallels, but it is also located at 77 º0’33”W on the meridians.
Its exact location would be 38 º 53’51”N, 77 º0’33”W.
At the equator, 1º longitude = 111km. However, as one moves toward the poles this changes because all meridians meet at the poles. This distance becomes smaller until it reaches 0 at the poles.

9. Great Circles Great Circles
Any circle that divides the globe into halves.
Any circle formed by two meridians of longitude directly across from each other on opposite sides of the globe is a great circle.
However, the equator is the only great circle for parallels of latitude.

10. Finding Direction Finding Direction
Magnetic compasses can indicate direction because the earth has magnetic properties.
Recall, the earth’s geomagnetic poles are offset from the earth’s geographic poles.
All compasses point toward earth’s geomagnetic poles, not geographic North and South Pole.

11. Finding Direction
The angle between the direction of the geographic pole and the direction in which the compass needle points is called magnetic declination.
We say “True North or True South” to indicate geographic north and south poles.
Magnetic declination has been determined for points all over the earth.

12. Example: Central Ohio is located at approximately 7ºW of true north
Example: Central Ohio is located at approximately 7ºW of true north. Example: Where is central Texas located according to true north?