NavList:

Frank:

I'm sure you'll get a lot of comments on this one.

I personally see the IDL as being in the same category as time zones -- something to make communications, shipping, and human interaction in general easier.  For example, before railroads every town on city in the USA had its own idea of local time.  Works fine when riding horseback.   But railroads needed something that was more precise and predictable -- imagine printing a timetable (or trying to coordinate the moment of trains) if each and every stop on the line had its own idea of what time it was.

I see the IDL the same way.  One of the ways I teach the IDL in offshore navigation classes is asking my students to identify time zones spreading out from Greenwich.   We go from ZD 0 to ZD +12 going westward.   We go from ZD 0 to ZD -12 going eastward.   Whoops, the zone that says "I'm 12 hours ahead of Greenwich" and the zone that says "I'm 12 hours behind Greenwich" abut each other.   What time is it?  12 hours ahead or 12 hours behind???

So I'm not sure the IDL can be described as a "map maker's fiction" so much as an agreed-upon line where today turns into tomorrow heading west or today turns into yesterday heading east.

I believe an intriguing piece of information would be what circumnavigators did before standardization of the prime meridian at Greenwich and, by implication, the IDL in the middle of the Pacific?   How/where/when did the navigator on a circumnavigating ship skip the date forward or backward?  

Lu Abel