A geographic coordinate system is a coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are often chosen such that one of the numbers represents a vertical position, and two or three of the numbers represent a horizontal position. A common choice of coordinates is latitude, longitude and elevation. 

To specify a location on a two-dimensional map requires a map projection. 

The invention of a geographic coordinate system is generally credited to Eratosthenes of Cyrene, who composed his now-lost "Geography" at the Library of Alexandria in the 3rd century BC. A century later, Hipparchus of Nicaea improved on this system by determining latitude from stellar measurements rather than solar altitude and determining longitude by timings of lunar eclipses, rather than dead reckoning. In the 1st or 2nd century, Marinus of Tyre compiled an extensive gazetteer and mathematically-plotted world map using coordinates measured east from a prime meridian at the westernmost known land, designated the Fortunate Isles, off the coast of western Africa around the Canary or Cape Verde Islands, and measured north or south of the island of Rhodes off Asia Minor. Ptolemy credited him with the full adoption of longitude and latitude, rather than measuring latitude in terms of the length of the midsummer day. QUESTIONS:

Q1:
1. What is a common way of determining coordinates?
2. How are coordinates usually chosen?
3. How does one normally calculate coordinates?
Q2:
1. How are geographic coordinate systems defined?
2. What is the definition of a geographic coordinate system?
3. What does the term geographic coordinate system mean?
Q3:
1. In a geographic coordinate system, how are the coordinates chosen?
2. By what metric are coordinates chosen in a geographic coordinate system?
3. How do you choose coordinates when you use a geographic coordinate system?
Q4:
1. What do you need to specify a location in a two-dimensional map?
2. When using a two-dimensional map, what is needed to specify a location?
3. In order to find a precise location on a two-dimensional map, what is required?
Q5:
1. Who is generally accepted as the creator of the geographic coordinate system?
2. Who is believed to have invented the geographic coordinate system?
3. Who is the generally accepted inventor of the geographic coordinate system?
Q6:
1. When did Eratosthenes create the geographic coordinate system?
2. In what century was the geographic coordinate system invented?
3. What century did Eratosthenes invent the geographic coordinate system in?
Q7:
1. Who refined the geographic coordinate system after Eratosthenes?
2. Who later improved upon the geographic coordinate system invented by Eratosthenes?
3. Who was able to improve upon the geographic coordinate system of Eratosthenes?
Q8:
1. How did Hipparchus of Nicaea improve the geographic coordinate system?
2. What did Hipparchus of Nicaea do to refine the geographic coordinate system?
3. What improvement did Hipparchus of Nicaea make to the gographic coordinate system?
Q9:
1. What contribution did Marinus of Tyre make?
2. How did Marinus of Tyre contribute to coordinate systems?
3. What was the role Marinus of Tyre in the field of geography?
Q10:
1. Where did Eratosthenes invent the geographic coordinate system?
2. In what location did Eratosthenes create the geographic coordinate system?
3. What was the location of Eratosthenes' invention?
