Monday, 30 May 2016

When is a map not a map

Friends of mine lived in London, then LA and now in Wellington, NZ. I wondered where their peripatetic moves might take them, in a purely geographic destination sense?

There's the lowest tech way is to stretch a string along a globe or to put a very large rubber band around it to go over three cities, then loop the loop and see where a fourth city may land? The red circles mark the quarter and half points along the string, so Mauritius seems to be the destination... not bad!

click to enlarge

Then there's the high tech way, to draw a great circle on a map to do the same:
  • This web map details the method, but basically since London and NZ are more or less antipodean, I searched the nearest settled place antipodean to LA (180+long. and -lat. of original long. and lat. in World Geographic WGS84 projection). Whilst that was in far south Indian Ocean, the closest places were Mauritius, Reunion and southernmost Madagascar so I picked Port Louis, Mauritius.
  • CLIWOC Gazetteer map had Greenwich (London), Sta. Barbara Channel (LA), Cape Campbell (Wellington) and Port Louis (Mauritius) as place names, so I subset a database to those four locations, reindexed them, added fictitious years and duplicated the columns to make from-to segments.
  • this resulted in a time-enabled map with points and great circles, modeled after my popular but far more complex Where in the World is Andrew map:

Note: no ESRI? Get ArcGIS for Home Use incl. ArcGIS Online for a Benjamin a year!

But do we really need a map to do all this, is there a way to google antipodes at all? Enter WolframAlpha (WA), a search engine that does math as well as text:
  • as above, I simply searched "antipodes LA" - try it and select the geometric option - and you land somewhere in the Indian Ocean - set the map window to 5000+ to see where you are - Island of Mauritius lies the closest and that sounded like a fun destination.
  • looking up 'great circle' you see that WA does circles too, and with a little tinkering I found this search: "circle London, LA, Wellington, Port Louis Mauritius".
  • accept the default syntax it interpreted your query as, and all the stats on distances and travel times are detailed, but this map caught my eye:

click above to enlarge, image source

It was fun to stretch a string on a globe, and creating a web map from previous experience took some time, but a search engine on steroids made short shrift of this after tinkering with syntax. The point is: always look for various ways to satisfy your curiosity... A map may be not what you think!

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