Comment by OscarCunningham
7 years ago
They use height data rather than land/water data, and assume that there's just a cutoff at sea level. I think this gives them the correct answer for the water path, but it gets things wrong for the land path because there are a lot of lakes and rivers above sea level and also some dry land below sea level.
If you don't allow the path to cross any lakes or rivers at all then I think the land path has to be much shorter, since rivers makes it impossible to make any progress at all in most places. If you trace their path it definitely goes through several lakes. The optimal path is probably across a desert, my guess would be Antarctica.
If you do allow the path to cross lakes and rivers then I think there's a longer path than the one they give, starting in Liberia and ending near Fuzhou, China. They probably didn't spot this one because it passes too close to the Dead Sea, which is below sea level (and crosses the Suez canal, which is at sea level).
> They probably didn't spot this one because it passes too close to the Dead Sea, which is below sea level
This is adressed in the paper. The relevant part of the problem statement: "the longest distance one could drive for on the earth without encountering a major body of water"
and about the Dead Sea: "Guy Bruneau of IT/GIS Consulting services calculated [5] a path from Eastern China to Western Liberia as being the longest distance you can travel between two points in straight line without crossing any ocean or any major water bodies. However, the path crosses through the Dead Sea (which can be considered to be a major water body), and hence does not satisfy the constraints originally set out."
Oh, I didn't spot that they had already considered that path.
However I don't accept their defence.
1) Depending on environmental conditions, my path can cross the Lisan Peninsula. https://en.wikipedia.org/wiki/Lisan_Peninsula (EDIT: In fact there's enough clearance to just go completely south of the Dead Sea)
2) Their path crosses the Volga River, which is much larger in total surface area than the Dead Sea. And at the point at which they cross it, the Volga is just as wide as the Dead Sea.
But rivers don't fit in the conventional definition of "major body of water" even if their surface area is large.
It's odd to say you "don't accept their defense" when you're really just operating from a different set of assumptions in the first place.
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Is that a straight line? Maybe they allow crossing rivers but not seas/lakes.