Geohashing Followup + change to algorithm for Europe, Africa, Asia, and Australia

Geohashing has been great fun so far. There are hundreds of users on the wiki, and I’ve gotten to wander places like this:

There’s been a small change to the algorithm to deal with time zones. This change does not affect anyone in North/South America (excluding Greenland), does not affect Saturday meetup times anywhere, and does not change any currently known upcoming meeting times. The change:

For every location east of Longitude -30 (Europe, Africa, Asia, and Australia), use the Dow opening from the previous day — even if a new one becomes available partway through the day.

Put differently (the same functionally for everywhere except islands in the mid-Atlantic):

Consider any Dow openings published after noon local time to have occurred on the next day.

This is necessary to deal with time zone problems. For a lot of Europe, the Wednesday Dow opening was learned near sundown Wednesday, which meant they couldn’t use it to get to daytime meetups. For east Asia, they had to visit weekday locations the next day. A bunch of solutions were discussed, and I decided this was the cleanest.

The official map tool is being updated with the new behavior concurrently with this blog entry. The first coordinates that will be affected by it are Tuesday’s. Again, this does not affect anyone in the Americas.

Moving on — Saturday’s meetups are looking good! Today’s location in Boston was fantastic. I wasn’t planning to go, but it looked so interesting on Google Maps that we couldn’t resist checking it out. The picture above is one of several. Saturday’s meetup is in a less picturesque place than Friday or Sunday — suburban Hopewell. We’ll probably gather only briefly at the actual point, then head to the nearby state forest for walking or town center for food and such.

Also, good luck to phire, who was last seen on IRC an hour ago, leaving to mountain-climb to today’s coordinates in Christchurch, New Zealand. Congrats to the Denver graticules for getting organized so fast (and in a split city, at that!). And thanks to everyone for going along with this idea! The weekday trips have been great fun so far, and I look forward to getting the meetups going over the next few weekends!

Geohashing

Summer seems to have arrived, at last.

As you may have noticed, today’s comic contains an algorithm for converting dates into local coordinates. For a given day, you can calculate what that day’s coordinate is for your region. Dan has put together a tool for calculating a day’s coordinates and show it using Google Maps. Note that you can’t calculate a day’s coordinates before the stock market opens on that day (about 9:00 EST) — except for weekends and holidays, when it uses the most recent opening price.

We’ve been having fun trying to reach these coordinates for some time now, when the coordinate is reachable — that is, when it’s not over water, in a military base, or in the middle of Bill Gates’s house.

If you happen to be looking for somewhere to go, driving to the coordinates can be an adventure. If you do, please take pictures and drop them on the geohashing wiki (feel free to help fill it out).  I’m gonna get some rest and then, at 10 AM tomorrow, see if I can get to the Boston coordinates (I have no way of knowing where they’ll be until then, of course).

And finally, when the coordinates are reachable, meetups are Saturday afternoon at 4:00.

Edit: I answered a bunch of questions in a comment below.  Further discussion is also happening on the wiki. I’m going to get some sleep and then head out to today’s coordinates (or as close as I can get).

GPS Cyborg Implant

Last week, I wrote a short Python script that uses a USB GPS device under Linux to help with navigation.  It doesn’t have maps or anything — it just gives distances and, while you’re moving, the direction to the destination (as in “two o’clock”).  It prints this info on the terminal and speaks it using speech synthesis.

I joked about this in Comic #407, but it’s actually a pretty practical way to get around.  Just knowing what direction something’s in is a huge step toward finding it.  This past week I’ve used it successfully to find my way around towns I don’t know, and we even used it while driving to navigate to an out-of-town destination.

Plus, there’s the bonus that when you’re walking, wearing an earpiece, laptop in the bag, listening to the computerized voice whisper “TARGET DIRECTION THREE O’CLOCK DISTANCE ONE POINT THREE KILOMETERS ETA FIFTEEN MINUTES” into your ear, you feel like a cyborg.  I’ll have to set it up with a female voice and rename it “jane.py”.

Edit: I’ve just been testing the recent changes to this script, and it’s really not in a condition where I should be posting it anywhere.  But if you can use it as a starting point for hacking, here’s the link.  Some of you might find it useful sometime soon.

Friday Night

So there I was at the stroke of midnight, contemplating the four-knights opening by the dim glow of a flashlight, ears popping under the extra five pounds per square inch of pressure.

MUSC (artist's depiction)

On Friday night, Dan (who you may remember as the Robot9000 bot author), Elizabeth and I invented midnight underwater speed chess.

A nice feature is the naturally-enforced clock.  You have as much time per move as you have air in your lungs. Protip: don’t use a glass set.

Now we just need to combine it with chess boxing.

Center of Population

What’s the world’s center of population?

The center of population for a region is, roughly, the center of mass of the inhabitants. The Census bureau defines the center of population of the US (currently in Missouri) as

the point at which an imaginary, flat, weightless, and rigid map of the United States would balance perfectly if weights of identical value were placed on it so that each weight represented the location of one person on the date of the census.

This definition breaks down for populations on curved surfaces. For the earth as a whole, the center of mass obviously falls deep inside the planet.

This problem is easy to fix. I figure a better definition would be the point at which the sum of straight-line surface distances to each person is minimized. This is equivalent to the standard definition for a flat region, but it has the advantage that you can use it to define the center of population for a sphere.

I’ve never seen anyone who’s calculated the earth’s center of population so defined, but it doesn’t seem like it would be hard. Does anyone have the answer?

Bonus: find the center of population for other groups. What is the center of population of native English speakers? internet users? … bloggers?

Edit: I was standing the shower just now when I realized that the generalization I was using had to be wrong. I got it from this page on Wolfram Mathworld,

The centroid of n point masses also gives the location at which a school should be built in order to minimize the distance travelled by children from n cities, located at the positions of the masses, and with m_i equal to the number of students from city i (Steinhaus 1999, pp. 113-116).

and did try to check out the citation while writing, but it was to a book and I was much too lazy for that. However, I think the Wolfram paraphrasing is wrong — it’s not the distances that are minimized; it must be some other quantity. You can see that this is wrong for center-of-mass of two people at A and one person at B. It’s probably sums of squares that are minimized (as suggested in a comment, and which works for the three-person example) but I don’t see an obvious proof of this.