Geography Reference
In-Depth Information
Withoutmodernmapmakingtools,scalecanbetricky.FrancisBillingtonwasateenager
when his family landed at Plymouth Rock in 1620, and records of the time make him out
to be the colony's Bart Simpson, an incorrigible juvenile delinquent. He nearly blew up
the
Mayflower
in harbor by firing his father's musket inside a cabin where flints and gun-
hilltopandwassurprisedtosee“agreatsea”threemilesaway.Thisdiscoveryledtoagood
deal of pilgrim excitement—could this be the famous Northwest Passage?—but when the
vast “Billington Sea” (as it is still known) was explored, it turned out to be a pond only
seven feet deep. Oops.
WhensoldierslikeZebulonPikeandStephenLongfirstexploredthehighplainsofKan-
sasandNebraska,theythoughttheregion“whollyunfitforcultivationand,ofcourse,unin-
habitable.” Pike wrote that the plains “may become in time equally celebrated as the sandy
desertsofAfrica,”andLong'smapevenlabeledthearea“
TheGreatAmericanDesert
.”As
a result, the plains were held to be valueless and settlers avoided them for decades. As it
turned out, the explorers had visited during a dry period in the region's drought cycle, and
of course they had no idea of
the vast
aquifers under their feet that made the area ideal for
irrigation farming. Today, the same region is called “America's breadbasket.”
I mention these misconceptions not to discredit the early map-makers but to show what
they were up against: they were writing the first records of every single thing they saw.
Their horizon was only three miles away, and they had no way to transcend the limits
of their own viewpoint. Consider the laborious process of making the first survey of a
region using eighteenth- or nineteenth-century technology. First you need to establish a
baseline—a precisely known distance between two points. Today you'd do that with a
laser; measure the time it takes light to reflect off a prism, and within seconds you'd have
the distance. But back then it meant inching across the countryside with a sixty-six-foot
chain, moving the chain like a football referee every time it got fully extended and always
taking great care to keep it straight and at a constant elevation (on wooden trestles, if ne-
cessary). Marking off a single seven-mile baseline could take weeks.
And
then
thefunwouldreallystart.Frombothendsofyourbaseline,youuseabulkyin-
strumentcalledatheodolitetomeasuretheangletoasinglelandmark—ahilltop,maybe,or
a distant church steeple. With a little tenth-grade trigonometry, you use the baseline length
andthetwoanglestocomputethedistancesfromeachendpointtothethirdlandmark.Well
done! You have just surveyed a single triangle! Now take one of your endpoints and the
new landmark, and make that distance the baseline of a second triangle, and one of that
triangle's sides the baseline of a third triangle, and so on. Now please try to resist blowing
your brains out when I tell you that the Great Trigonometrical Survey that mapped Brit-
ish India two centuries ago required more than
forty thousand triangles
to complete and
stretched from a five-year project into an eighty-year one.
*
