1. The Earth and Earth Coordinates We’ve known for over 2000 years that the earth is spherical in shape Aristotle in the 4 th century BC believed that the earth’s sphericity could be proven by careful visual observation The Greek scholar Eratosthenes made the first scientifically based estimate of the earth’s circumference 1

2. 2Figure 1.1

3. 3Figure 1.2

4. 4Figure 1.3

5. Latitude & Longitude Putting latitude and longitude together into what is called a geographic coordinate (45 o N, 120 o W) pinpoints a place on the earth’s surface The latitude and longitude of the North Building 68 th Street courtyard is: –40 o 46’ 05.64”N, 73 o 57’ 52.29”W 5

6. Latitude & Longitude Latitude and longitude locations can also be expressed in decimal degrees through the following equation: Decimal degrees = dd + (mm / 60) + (ss / 3600) mm is the number of minutes –ss is the number of seconds –for example: –44 o 56’ 18” = 44 + (56 / 60) + (18 /3600) = 44.9381 o 6

7. Latitude & Longitude Decimal degrees are often rounded to two decimal places so the location of the North Building 68 th Street courtyard would be: –40.92, -73.97 7

8. Prime Meridians In the 4 th century BC Eratosthenes selected Alexandria as the starting meridian for longitude In medieval times the Canary Islands of the coast of Africa were used since they were then the westernmost outpost of western civilization In the 18 th and 19 th centuries, many countries used their capital city as the prime meridian for the nation’s maps 8

9. Prime Meridians Pirate Maps…….. Prime meridian problem was eliminated in 1884 when the International Meridian Conference selected as the international standard the British prime meridian 9

10. The Earth As An Oblate Spheroid Scholars assumed that the earth was a perfect sphere until the 1660s when Sir Isaac Newton developed the theory of gravity 10

11. Figure 1.411

12. Figure 1.512

13. Historical and Current Oblate Ellipsoids 13

14. Ellipsoids The World Geodetic System of 1984 (WGS84), replaced the Clarke 1866 ellipsoid in North America and is used as the basis of latitude and longitude on maps throughout the world 14

15. Figure 1.615

16. Figure 1.816

17. Figure 1.917

18. Figure 1.1018

19. Figure 1.1019

20. Figure 1.620

21. 21Figure 1.3

22. Figure 1.1222

23. Figure 1.1523

24. Figure 1.1624

25. Figure 1.1725

26. Figure 1.1826