Latitude / Longitude and Your GPS

Since the beginning of man’s time on Earth, he has recognized the need to “navigate” whether it be on dry land or on the sea (and now in outer space). Early man started with a list of waypoints, augmented with crude estimates of distance and time. These lists, when used at sea were known as “Sailing Lists”, and have evolved to a modern form still in use. Of course today, a modern captain makes use of charts and an array of electronic tools to find his way.
Successful navigation requires an understanding of speed, direction and time, and at sea, it requires knowledge of water depth. Techniques to measure these requirements have evolved over centuries of mathematicians, engineers, astronomers, and sailors. Earliest reference to a compass-like device can be traced back to Hannibal in 203 BC. Norsemen of the 11th century are recorded to have used a direction-finding device, and records of a compass have been found, dating back to the year 1200.
Early man made use of the stars, sun and moon to aid in finding his direction. It’s interesting, that the original “North Star” was not Polaris. Rather, a star called Draconis was used (17th century BC). Using early forerunners of the sextant, the navigator was able to find his latitude position along a north-south meridian, by measuring the angle of a celestial body above the horizon. He soon learned to also find his east/west position as well.
The age of iron ships brought on a problem for the compass, which was addressed by the invention of what we know today as the “gyro-compass”; originally called the “Rotascope”. However, a method of keeping the rotating gyro in motion was a problem which wasn’t resolved until the use of electricity, some 50 years later.
Early man initially measured his speed through the water with the “Log” which eventually became known as the “Chips Log” or “Ship’s Log”. It initially involved throwing an object overboard, and observing how much time passed as the vessel moved by. Simple math computations converted the results to “Speed”.
Then came the idea of tying a line to the object, with equally spaced knots tied into it. The object was thrown it over the stern, and as the line passed through the hands of the seaman, he would count the knots as he recited a script. The script was used to measure time. Thus the term “knots” entered the picture. Eventually, other mechanical methods were developed to measure speed as well.
All this time, another group of folks was observing the sky. They discovered (and documented) movement of the planets, the sun and the moon. Eventually, they were able to measure the size of the Earth. The accepted value for the circumference of the Earth, or length of the Equator, varied over the centuries. For purposes of creating charts, the length of the Earth’s Equator (circumference of the Earth’s sphere) was divided into 360 equal parts, which represented degrees of a circle when viewed from above the North or South Poles. If a line (meridian) is drawn from the North Pole through the Equator, and terminating at the South Pole, through each of the (360) degree markings of the Equator, and terminating at the South Pole, we would see 360 lines of “Longitude.”
The same logic was used to draw parallel lines to the Equator. Only this time there are 90 numbered lines in the Northern Hemisphere starting with zero (0) at the equator and ending with 90 at the North Pole, and the same on the Southern Hemisphere. Each number-label represents a degree of “Latitude”. If we were to draw these lines on the globe in your family room, they would form a grid of squares on the surface of the globe.
Each degree of Latitude and Longitude is further divided into 60 “minutes”. Each minute is further divided into 60 seconds. A value of distance was then assigned to each Minute of a degree of Latitude, to be one (1) Nautical Mile.
But as the chart-maker folks began seeking a value for their Nautical Mile, which is based upon the size of the Earth, they found a variety of cities in ancient Greece, and the Roman Empire were using different values for the length of a statute mile (over land). This became a problem.
This is a short version of why we have “Statute Miles” and “Nautical Miles”, and as it turns out:


Speed on nautical charts is calculated in “Knots”, whereby

Therefore, Miles Per Hour (MPH) on your car’s speedometer is not the same as Knots (Kn) on a boating instrument.
There were various methods used to chart (map) what was discovered on our planet Earth. But, the spherical shape created in-accuracies when drawn on a flat piece of paper. Eventually all of these obstacles have been dealt with.
Units of measure continued to be vague over the centuries of early civilization. Man used what he had to make measurements, such as the width of a finger, the span of his hand, the distance from his elbow to the tip of his middle finger (Cubit), or the distance between his outstretched arms (Fathom).
Today we have overcome the confusion of measured values. We have standards for weights and measures that are well documented over the world, and we have accurate machines and instruments to measure with.
BUT WAIT ! A NEW PROBLEM HAS ARISEN. Remember the discussion of Latitude, Longitude, and how it’s documented in degrees, minutes and seconds? This all works really well, until the introduction and mass distribution of land-based GPS devices, such as your car’s navigation system and your “smart-phone”
I personally downloaded a couple different “apps” on my smart-phone which are advertised to provide Latitude and Longitude of my position, here on Earth. Turns out, some of these “apps” work differently. Some provide my location in degrees plus the decimal portion of the next degree.
For example: 28.500 degrees N This would be 28 degrees plus ½ the distance to 29 degrees. (Remember, a degree is divided into 60 minutes, and each minute equals one nautical mile.) So….. This location would be 30 miles North of the 28th degree of Latitude.
But, what if we read the 28.500 N as a trained navigator, would normally refer to a latitude position? The navigator is trained to work with coordinates written in degrees, minutes and seconds: 28 degrees 50 minutes 0 seconds This position is located 50 nautical miles North of the 28th Latitude; a full 20 miles difference ! If you are seeking assistance from a rescue crew, they won’t find you here.
The point is………. If you are giving your position coordinates to request assistance, or any other reason, then know (and understand) what you are reading. The new phone “apps” and automotive navigators are not necessarily intended to be used at sea.

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