Re: [Paddlewise] UTM

Thanks for the link <http://www.nps.gov/prwi/readutm.htm>.  That 
Mercator thing is very well explained.

It is not a question of which is better, but which is more useful
for different purposes. 

For land, where measurements require precision of less that 1/4 inch,
UTM was made to reduce spherical distorsion in small areas and
make plotting easier. That way, if two neighbors are fighting for
a centimeter of land, the boundaries can be defined with great
precision.

At sea, 1 second of latitude is 1/60 of a nautical mile. That is 30
meters, or the length of a medium size recreational sailboat. 
See? The precision of the latitude/longitude system is already more
than what most mariners need. 

In addition, mariners are more
comfortable using knots for speed, and nautical miles for distance,
all of which refer to the length of 1 minute of latitude.

So, why degrees instead of meters?  The strongest argument is
probably celestial navigation.  With celestial navigation, every
measurement of a celestial body's height in degrees is used
to solve a triangle on the earth surface using trigonometric formulas.

Now that we have GPS's, we could change all systems to a unique one
based in meters.  But then, your life would depend on the batteries
of an electronic gadget, and we would have to redo years of work
of coastal survey.  It is probably easier and safer to stay with
our current system, which is known to work for all mariners.

In summary, precision measurements on land benefit from the 
mercator system, and navigation at sea benefits from the degree system.

Good GPS's carry both systems.

Happy paddling,

- Julio
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