On a recent trip up the Oregon coast, a friendly doorman at our
hotel in Portland was inquiring about our trip. When we mentioned we
passed through Bandon, OR, he quipped that Bandon was the place
furthest from a city of one million people in the USA. I guess a
normal person would just think "oh, that's interesting" and move on,
but it has been plaguing me ever since.
Firstly, I had to find what cities in the USA had more than 1
million people. Luckily
Wolfram Alpha gives the answer:
- Chicago,Illinois
- Dallas,Texas
- Houston,Texas
- Los Angeles,California
- New York, New York
- Philadelphia,Pennsylvania
- Phoenix,Arizona
- San Antonio,Texas
- San Diego,California
(I certainly wouldn't have guessed that list!) From there my plan
was to find the bounding box of the continental USA; luckily
Wikipedia
has the raw data for that. Combined with the latitude and longitude
of the cities above, I had the raw data.
I couldn't figure out any way better than a simple brute-force of
testing every degree and minute of latitude and longitude within the
bounding box and calculating the distance to the closest large city;
the theory being that from one particular point you would have to
travel further than any other to reach a city of 1 million people.
Luckily, that is short work for a modern processor, and hopefully the
result would be a point somewhere around Bandon. I'd already become
acquainted with the great circle and measuring distances when I did
Tinymap, so a quick
python
program evolved.
However, it turns out that the program picks the far south-east
corner of the bounding box. Thanks to the shape of the USA, that is
way out over the ocean somewhere. I can't figure out a way to get an
outline of the USA to test if a given point is inside the border or
not, but all is not lost.
I modified the program to output the the distance to the closest
large city along with the location to a log file, and then imported it
into gnuplot to make a heat-map. The hardest part was finding an
equirectangular outline of the USA to place the heat-map over, rather
than a much more common Mercator projection;
Wikimedia
to the rescue!
I actually surprised myself at how well the two lined up when,
after a little work with Gimp, I overlayed them (
big)

From this, I can see that Bandon, about a third of the way up the
Oregon coast, is a pretty good candidate. However, probably not the
best; I get the feeling the real point that is the furthest from any
city of 1 million people is actually somewhere in the central-middle
of Montana.
However, we can also fiddle the program slightly to disprove the
point about Bandon. The numbers show the closest large city to Bandon
is LA, at ~1141km. Taking another point we suspect to be more remote;
the closest large city to Portland (where we met the doorman) is also
LA at ~1329km. So to reach the closest large city you have to travel
further from Portland than Bandon, so Bandon is not the
furthest place in the USA from a city of one million people. Myth
busted!