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> -----Original Message-----
> From: Frank Reed
> Where should one draw the lines? Does it make any
> difference? Should the date line be the simplest, shortest line
> that separates islands and land masses with differing date
> standards? If I'm a cartographer, can I draw the line anywhere I
> want (with due respect for tradition so I don't annoy potential
> customers)? Is there any practical circumstance where the
> arbitrariness of the date line might eventually cause problems??

Frank, I dug into IDL history and tradition a fair bit last year, when I was
working on
http://jimthompson.net/boating/CelestialNav/DatesTimeDiagrams.htm
and
http://jimthompson.net/boating/CelestialNav/CelestNotes/Time.htm

As I understand it, the IDL and in fact all time zone boundaries are not
mandated by any international law.  So land communities can set their own
legislation to define where they draw their time zone boundaries, and define
which time zone they lie in.  Hence there are many zig-zags and odd pockets
of local time variances from the basic concept of even longitude boundaries
every 15 degrees.  These boundaries change so frequently around the world
that keeping a map perfectly up to date is very difficult.

Conversely early in the 20th century an international convention was struck
whereby ships at sea were to honour the "Nautical" Date Line, which follows
the 180d longitude without zig-zagging.  One consequence of this is that
they used Time Zone Y in celestial navigation solutions.  I don't think any
land community lies in Time Zone Y -- perhaps Eniwetok.

I don't know if this was what you were looking for.

Jim Thompson

   

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