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Explanation of Latitude and Longitude
Globally all places can be located by a combination of two numbers, the Latitude and Longitude. The numbers measure the angles from the centre of the earth to a point on its surface. Latitude and Longitude values are expressed in Degrees(°) which for greater accuracy are in turn divided into Minutes(') and Seconds("). Each degree is divided to 60 minutes, each minute to 60 seconds; seconds are divided decimally to 1/10s, 1/100s. Latitude and Longitude values are expressed either:
Lines of Latitude and Longitude are theoretic lines on the Earth's surface; Latitude lines are horizontal, Longitude lines are vertical. Consider the spherical shape of the Earth, the North & South Poles and Equator.
Explanation of Latitude (Lat): The Equator is the Latitude Line of 0 degrees. Latitude values define the angular distance from the Equator to points North and South of it. From the Equator, there are 90 degrees of Latitude north to the North Pole and 90 degrees south to the South Pole. Latitude values north of the equator (Northern hemisphere) are assigned "N" and are positive values, those south of the equator (Southern hemisphere) are assigned "S" and are negative values. Lines of Latitude run parallel to the Equator (hence termed "parallels") and are "equally" spaced (the earth is not perfectly spherical so variation occurs) in that 1 degree of Latitude is approximately 69 miles.
Explanation of Longitude (Long): The Prime/Greenwich Meridian is the Longitude Line of 0 degrees. Longitude values define the angular distance from the Prime meridian to points East and West of it. There are 180 degrees of Longitude east and west of the Prime Meridian. Longitude values west of the Prime Meridian (Western hemisphere) are assigned "W" and are negative values, those east of the Prime Meridian (Eastern hemisphere) are assigned "E" and are positive values. Lines of Longitude ("meridians") pass through and converge at both Poles; every line of longitude crosses the equator. The 180 degree meridian on the opposite side of the world to the Prime Meridian, is not "E" or "W"; it is where the east and west hemispheres meet, the International Date Line. At the equator 1 degree of Longitude is approx 69 miles, but decreases progressively to 0 at the poles where the meridians converge. Accordingly 1 degree of Longitude varies in size; this is shown below for the land mass of UK & Ireland, located in round numbers in the Latitude range 50N ~ 60N degrees.
The Shortest Distance using Latitude and Longitude
To calculate the shortest distance between 2 places using the Latitude and Longitude values of the places, use the "Great Circle Distance Formula". The formula can be "simplified" by adjusting it to convert degrees to radians. If you require the distance between the 2 places expressed in miles, define the radius of the Earth ("R") as 3963.1, use 6378.7 if you want the answer in kilometres.
Use data table below to validate your formula and syntax. The table shows 4 pairs of locations, the Lat/Long values for each "Location 1" ("From") and "Location 2" ("To"). The examples use Lat/Long values of locations in the UK & Ireland land mass, deliberately including points either side of the Prime Meridian hence +/- Long values. Your answers should agree those shown below in the column "Distance in Miles".
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