Geohashing

Posted byRandall 586 Comments on 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).

586 replies on “Geohashing”

  2. It seems the Salt Lake City, Ut coordinates are over the Utah Lake. I think I’ll check again next week.
    Are there any other Utahers here?

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  3. Too bad for the people living in western gothenburg, about 95% or so of their square is just sea. Thankfully I live about 2 km east of the line.

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  4. For smaller towns (Newmarket Ontario for me) would it be recommended to used the coordinates for a closer and larger city, (such as the Toronto/Hamilton coordinates 1 deg south) or stick with a more accurate location with a (most likely) much smaller turnout?

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  5. pretty cool, works good for vancouver, sent me to the middle of golden ears provincial park from surrey central mall
    going to be fun trying to get there :3 [considering i walk everywear and have school today, plus replacing my motherboard]

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  8. I’m within 4,000 feet of the intersection of 4 regions, so I think I’ll take my choice of the 4 meetup locations. Today, my options are:

    1) an empty lot across the street from a golf course (I vote going to the golf course)

    2) In a lake, right next to a bridge… let’s start at the bridge before everyone gets themselves wet.

    3) Something with green plants… hill? bog? hunting grounds?

    4) Someone’s field.

    Sounds like a great time wherever I go!

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  9. Ugh, My zone is terrible, You quartered up columbus and now Im right in the corner, half the time my coords are in the deepest of boonies 50 miles away

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  10. Ugh columbus is quartered up and im right in a corner, now the coords are always 50 miles away in the boonies

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  12. Hmmm, the one east of Calgary today is right near my freinds cabin. Goddamnit work, I almost had an excuse to go camping.

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  13. Hmmm. My co-ordinates for today put me in the northern part of the Camp Pendleton Marine Corps base. Think they’d refrain from shooting me if I took a printout of this blog? 😉

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  14. So, for my box, most of the coordinates are about halfway between here and the college I’ll be attending in the fall.

    Something tells me I’ll be making a few extra road trips… XD

    Also, Cogito: You and I share the exact same birthday. Which officially makes you awesome.

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  15. I don’t think that the graticules should be used,

    Instead some common rectangles of land could be agreed upon in the wiki and used for particular cities.
    mattender seems to already presented a possible solution for this idea http://blag.xkcd.com/2008/05/21/geohashing/#comment-18498

    I would also argue about using the current days DOW open as part of the hash, it has 3 problems, A- it’s only present 5 of 7 days, and B-it’s not appropriate for many people due to the day being mostly over, and C-people have no time to plan and organize meeting up ( or location rejection – due to military base etc)

    I might propose something more earthy, like the 7th previous day’s seismic data , that way everyone has a week to prepare for a meetup, really, even something like the a particular airports weather data would work great, and each city could then use their own weather as part of the hash so that each “box’s” people aren’t going to the upper right corner.

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  16. Excellent! I’m in the same region as Randall. I’ll go if one’s close to me!

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  18. why did you have to plan the first one on the same day as the free CAKE and English Beat show? hopefully it’s close by so I can do both

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  19. What a freakin’ fantastic idea. Well done!

    Calgary’s another place that’s divided amongst four “hashpatches”. 51°N passes along 42 or 44 Avenue S., and 114°W is represented by either 24 Street E, Barlow Trail or the creatively-named Meridian Road

    Today’s options include:
    • The Morley reserve, about ½ mile from Highway 1A (NW)
    • A corner lot on Shore Drive, just off Range Road 284 (NE)
    • Ranch land west of Stavely, a couple of miles away from SR 527 (SE)
    • Fording, BC, about 10 miles north of Elkford (SW). This is probably 250 miles of driving from Calgary, thanks to the mountains. Just a leisurely afternoon stroll, indeed 😉

    I see that Washington DC has been mentioned as another location with this problem, and I’m certain there are other cities divided by whole number lat/long lines, thus are positioned across 2 or 4 patches. My proposed solution to this problem is:

    When the decimal portion of the latitude is less than .500, the marker will lie in the south half of any given square degree, therefore the north hashpatch is closer. When the decimal is .500 or higher, the converse is true, so you’d head south. Do the same for longitude, and go east or west as appropriate (Cities divided along only one axis obviously only consider one of the above)

    If today were Saturday, I and other Calgarians would go north, since the designated latitude is xx.179 ( .500), taking us to the Shore Drive location mentioned above

    So you get kind of a Mah-Jongg thing going here, where one tile is placed overlapping 2 or 4 beneath it. You only concern yourself with this one central overlapping tile and the area it covers, which keeps these trips within a more feasible distance and hopefully maximizes the number of people who come out and attend

    If I remember when I get home, I’ll clean this up and repost it to the wiki

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  20. Heh. Sadly, this doesn’t work for my location.

    There’s too much water near where I live, so today’s spot is eight miles off the coast into the bay.

    Captcha: Ceremony Evacuated. … Now isn’t THAT forboding.

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  21. Hmm. Something went wrong. That’s what I get for using HTML tag brackets as less/greater than signs

    That sixth paragraph (If today were Saturday . . .) should read:

    . . . xx.179 (lt .500) AND east, since the longitude is yy.682 (gt .500), taking us . . .

    Oops 😉

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  22. This sounds like great fun. ill have to check where seattle’s ends up this weekend!

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  23. To people who are whining about locations being too far or too difficult or not having enought time: thats half the fun. Its an adventure, not a meet organizer. There is a whole subforum for planning meets if you want to plan something and have input into the time and location.

    I for one am in Randall’s area and today’s location in Auburn is very close to my parent’s house. 🙂

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  24. Locations being too far away….

    is england a bit far?

    Don’t think it’ll work with most of you guys.

    I’ll have to see if anyone around here is. Being on an island could be a problem even if it is a big one.

    Sigh….

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  25. Hmm… According to the map, today’s (May 21) destination for everyone in New York City (aside from those in the Lower West Side of Manhattan) is in the Atlantic, a few miles out from the Jersey Shore. And given the proportions of the area, roughly 2/3 to 3/4 of all destinations would end up in water.

    I view this as proof that Randall’s Boston bias leads him to want to murder NYC readers.

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  26. A mountainside. In Kerry. At least two hours drive away. Well that’s just great.

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  27. I think that the scheme, as presented, will only ever produce positive offsets from the integer location. It seems like, to make a more interesting game of it, the decimal portion should be multiplied by two, subtracted by 1, and then added to the full coordinate of the current location.

    So, in your example:

    (0.857713 * 2 – 1), (0.544544 * 2 – 1) = (0.7154260, 0.0890880)
    then adding to the full coordinate of current location:
    (37.421542, -122.085589) + (0.7154260, 0.0890880) = (38.1369680, -121.9965010)

    Otherwise you’d always be going southwest. 🙂

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  28. Okay, I realize the flaw in my reasoning. If the goal is to produce a single location for people from differing, but nearby, locations to meet – you kinda _have_ to discard the decimal part of the start location. And you want to produce a destination location that’s in the same “bin” as the collection of start locations. So the original algorithm is bueno, and I am totally wrong! I withdraw!!!!

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  29. @boazg:
    >> While i like the idea, i unfortunately live in Israel, where this algorithm completely fails. The odds that a point will fall inside Israel, in a safe place, are rather slim.

    I am working on an Israeli version, will be ready tomorrow (thursday). Stay tuned!

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  30. Seems to me that, once a day’s Dow data is available and the decimal offsets can be calculated, it’d be trivial to display them *all* on a map, so folks who live near a boundary or near water could easily see where the neighboring points are and pick one that looks safe and legal.

    Also, in the case that the point lands in the water, why not just meet on the shore, at the correct latitude but the wrong longitude, in the case of a north-south shoreline, or the correct longitude but the wrong latitude, in the case of an east-west shoreline?

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  31. Next weekend day that I’m in town and the meetup point is in the middle of San Francisco Bay, I will be there.

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  32. Trying to find the spot for the Columbus, Ohio area but I am not sure how this is supposed to work. Any help for the n00b?

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  35. I don’t know if you’ve had time to figure it out for yourself yet or not, Dan, but the reason a different location turns up for Fridays, Saturdays and Sundays is because the date, and not just the DOW figure, are both thrown into the hash.

    Due to a bit of avalanche effect, the change of that one number, by just one means an entirely different hash (a significant intention behind MD5) and therefore a completely new “Random” location.

    So that raises the question, should the meeting place be based upon Friday or Saturday’s date?

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  36. Ahh, this is so excellent! Although, I have the same question as the one above me, should meet-ups be based on Saturday or Friday’s date?

    That aside, though, I look forward to many a summertime adventure. Thank you, Randall Munroe. 😀

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  37. I like the “mah-jongg” idea, Gylbert, and would recommend it for the Chicago area (most of the city is in one graticule, but the metro area as a whole is more or less split into four — plus this would take care of the whole “my meetup location is in the lake” problem.)

    Today’s Options in Chicagoland are:

    Quadrant I — Somebody’s house in Deerfield. Probably wouldn’t appreciate people tromping through their back yard, but there is a park w/a baseball diamond just down the road. Incidentally, this is one of the few times this quadrant won’t produce a “seaplane” result.

    Quadrant II — Conveniently located on a road, but so far in the middle of nowhere that the satellites won’t go to maximum zoom. Supposedly near “Irene, IL”, though I’m not sure that’s a real town.

    Quadrant III — See Quadrant II

    Quadrant IV — What appears to be a farmer’s field just off of I-57, on the northern edge of Bourbonnais.

    Under mah-jongg rules if this were Saturday, we’d meet up in Deerfield, which seems reasonable. Though I wouldn’t stop anyone from taking photos out in those fields!

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  39. > Finally, all my stock market manipulation has a purpose! Let’s see if I get this in my living room…

    I thought of that – but you need to break MD5 as well. By tomorrow.

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  40. Unsurprisingly, my quadrant includes a full 98% of the state of Rhode Island. It would suck for anyone in Montauk who wanted to meet up, though.

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  42. This reminds me of Close Encounters of the Third Kind, like when they got the coordinates to go to Devil’s Tower…It’d be funny if that became one of the meeting places…

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  43. Pingback: Geohashing « Visible Procrastinations

  44. The Newark graticule is pretty good. That’s the one to the west of the NYC graticule, that picks up Battery Park, Red Hook and Staten Island, and the triangle of Pennsylvania that sticks in near Trenton. Mostly, though, it’s north Jersey. Almost all landmass, except for Raritan Bay. In fact, I speculated on the wiki that this one could very well be the most densely populated graticule in the United States.

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  45. Hmm… I’m stuck with Lake Ontario in the middle of my region. About 60% of the time, the location is out in the middle of the lake. If only the algorithm could be set to avoid water… Maybe by using a coordinate system only defined on dry land?

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  46. Hey anyone in the Oregon-esque area thinking about going? My lil bro and I are thinking of doing it, either the portland one or near Salem

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  48. I have a whole different problem than most people here….being Jewish, I can’t really travel on Saturday, which is our holy day. I’d love to go out adventuring, and wind up in some place I didn’t know existed, filled with fellow xkcdians – but I can’t do it on Saturdays. >_<

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  49. Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!Wibble!

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  50. Tamir, not that I’m an expert on Jewish Law, but doesn’t the Sabbath end at Sunset? This would allow you to turn up several hours late and find the pub that they all wandered off to…

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