Pathways
We define where we are on earth by several grid systems. The most common of these is latitude and longitude. Latitude and longitude divide the earth up into a series of parallel lines (latitude) and vertical lines running from the north pole to the south pole (longitude). Your book has a very good description of latitude and longitude, so read it carefully.
The base lines for measuring latitude and longitude are the equator and the prime meridian (see the graphic below).The equator goes around the middle of the earth, or it is the longest circumference. The prime meridian is an arbitrary line of longitude, but it was picked to go through Greenwich, England, the location of the Royal Observatory. Latitude is measured from 0 to 90 degrees north of the equator (0 to 90N), and 0 to 90 degrees south of the equator (0 to 90S), with 0 being the equator. It is easy to remember this by thinking about 180 degrees in a hemisphere, or half circle. Longitude is measured from 0 to 180 degrees east of the Prime Meridian (0 to 180E) and 0 to 180 west of the Prime Meridian (0 to 180W). Therefore, everything in the United States has a northerly latitude (it is in the northern hemisphere), and a westerly longitude (it is in the western hemisphere).
Increments of latitude and longitude are called ‘degrees’. One degree is divided into 60 minutes (‘). One minute is divided into 60 seconds (“). So a location might look something like this: 37º15’ 23”N, 122º14’8”W (where is this?).
Conduct some research about the relationship between time and longitude. Each 15º increment in longitude equals one hour of time on earth. We have roughly divide the earth up in this manner by time zones. You can therefore roughly estimate (ignoring daylight savings time and the peculiarities of political gerrymandering of time zones) how many hours earlier or later one location is from another. For example, if you were in a ship at 20ºW and you sailed to 80º W, what time would it be in your new location if it was 6pm in your old location? You would have traveled 60º to the west, so 60/15 = 4, and west equals earlier, so it would be 2pm in your new location.
The world is littered with imaginary lines: the Equator, the Prime Meridian, the International Date Line, the tropics, the polar circles, the Paris Meridian, the American Meridian – all are based on the basic grid of latitude and longitude that we are so used looking at on maps. There are, however, two imaginary lines that are incredibly fascinating but little acknowledged.
Source: Sobriera, http://upload.wikimedia.org/wikipedia/commons/8/82/Lines_of_equal_latitude_and_longitude_FROM_%28World_borders_parallel.png%29.PNG. Used under the Creative Commons Attribute 3.0 Unported licence.
The two lines you see crossing each other at the Equator and touching again at the poles in a figure-eight are the lines of equal latitude and longitude (really, it’s just one line that loops, but it’s easier to deal with by referring to it as two).Each point in the line represents a spot where the degree value of the line of latitude is the same as that of the corresponding line of longitude (e.g. 33.313°N, 33.313°W). Because of the nature of geographic coordinates (there are distinct locations for 90°N and 90°s, but 180°W and 180°E are one and the same), the lines of equal latitude and longitude only occur on one side of the Earth, necessarily centred around the Prime Meridian (0°).
The lines cross 19 different countries: 13 in Africa, 5 in Eurasia, and Canada. They also, of course, traverse Antarctica across the South Pole. Surprisingly few cities lie directly on the lines; Batumi, Georgia on the Black Sea and Hibberdene, KwaZulu-Natal on the Indian Ocean in South Africa being the most notable. There are a few significant near-misses including Maseru, Lesotho; Abidjan, Cote d’Ivoire; Abuja, Nigeria; Cairo, Egypt; and Orenburg, Russia.
The most interesting fact about the lines of equal latitude and longitude may be the utter lack of awareness of it: a Google search only brings up the Wikipedia article and links to said article. At least when it comes to the intersections of primary degree confluences of equal value (e.g. 6°N, 6°E, 7°N, 7°E, etc.), we can turn to the always informative Degree Confluence Project for information