Talk:Main Page

You shouldn't allow people to edit the Main page :-P

Saturday Times

Um the blog post says the meet ups are at 4, the wiki says they are at 3, is one time more official?

We were still going back and forth and the wiki hadn't been updated. For now, 4:00 -- closer to dinner :) Xkcd 06:55, 21 May 2008 (UTC)xkcd

Europe Time Zones problem

It seems there are two main proposed solutions. One is to use yesterday's stock openings for regions where the NYSE open is too late in the day, and the other is to use the Nikkei/London for east Asia and Europe respectively. We'll make a decision on that later tonight after reading over all the discussion. If you have an opinion, voice it here. --Xkcd 09:50, 21 May 2008 (UTC)xkcd

9:30 AM EST is 04:30 PM CET. So for us europeans it's half an hour or even 1½h after meet up times... :(

So what's a sensible Europe policy? If we can come up with something reasonable we can certainly adjust the tool. (The time zone stuff always makes my head spin a little).

Perhaps we should have anyone east of the Atlantic, up to a point, use the previous day's stock opening. Anyone in Europe have any thoughts?

I'm sorry for missing the point, but 9:30 AM EST on Friday is, by my calculation, 13:30 UTC, so with daylight saving taken into account: 15:30 (3:30PM) in central europe, on Friday. That would give us more than enough time to organise meetups on Saturday, right? The question is: do we do meetups at 3 PM local time or EST? - DWizzy

Indeed, how inconsiderate. We could, ofcourse, just say we use the previous day coordinates. Another option would be to use the numbers of a local stockmarket, but that could be a problem here, in the Netherlands, where I live. The country is quite small, and the chances of the meeting point being in one of the neighboring countries (especially Germany) are significant. However, if the Germans use their own stock market, they would have a different meeting point, possibly even in the Netherlands. Since it doesn't really matter which stock market we use, nationalistic feeling aside, we could just pick any one of them, or use the sum or some other calculation of various stock markets. -Sparky

Well, we want to pick something as simple and universal as possible. Some kind of EU market sounds reasonable; I hadn't really thought about that. It'd be nice if there were an elegant global solution that just involved a simple change ... if people here can get a consensus, we'll change the tool for handling Europe better. --Xkcd 07:36, 21 May 2008 (UTC)xkcd

Ideally, the global solution would be to use a market as far east as possible, so that everyone has the co-ordinates in time. But this happens at roughly the same time that the Dow closes the previous day, so that might be easier. It would give people in the western hemisphere a longer time to plan their trip than those in the east, but even New Zealand would get the number in time. -- Zephyr

That could, ofcourse solve the problem, but it's basically the same thing as using the previous days location if you're east of the Atlantic. - Sparky

Of course; but the pedant in me dislikes the idea of having a different algorithm depending on whether one is in the Americas or not. Actually, I suppose it isn't, if only the javascript interpreted "most recent" correctly :) -- Zephyr

Maybe just enter full time with local timezone as a reference time. I mean in the webapp you enter your local, timezoned time. The algorithm converts it to the stock market timezone and counts the latest opening before that. Geohashers around you are more than likely to use the same timezone, as you, so they will get the same location. No problem. Just enter Saturday, 4PM CEST (or whatever TZ you live in now) and you get *some* *predictable* stock market opening. - Tadeusz

Unfortunately, there's no way to have a real "global" solution when using a local stock market. Some random number source from space would work, but would be boring, and too hard to discover. I like the stock market idea. How about this:

• Hawaii to Newfoundland (UTC -10 to UTC -3.5) uses the Dow Jones
• Greenland to India (UTC -3 to UTC +5.5) uses Euronext 100
• Bangladesh to Micronesia (UTC +6 to UTC -11) uses the Nikkei 225

Calculating the local timezone is an exercise left to the reader... -Lucky

I agree about the no-real-global-solution point and in liking the stock market idea, but I don't see why random numbers from space would be boring. The md5 hash deprives the stock market index of meaning -- the only value is the fact that the number doesn't come into our knowledge until a predictable time in the morning. Maybe we can think of something intrinsically local per location? Like the opening value of your country's currency? —Christian Campbell 09:42, 21 May 2008 (UTC)

there are currently, I believe, 6 'areas' covering The Netherlands, but we could always decide to rotate fairly between those coordinates - with, as a bonus, we have a backup location when one is unreachable. I'd say, leave that to the locals. -DWizzy

I am in favor of the "use the DOW of the previous day" solution. This makes the tool simpler, and the point distribution around the globe uniform. - Sec

I'm not quite sure what to make of it. For Central Europe (I'm Dutch myself) and everywhere else I can't see why we wouldn't just pick a stock market on twelve hours distance from the Dow. As for Dutch meetups I'm all for cycling through the different areas as to get more people at one meet. Nazgjunk 09:24, 21 May 2008 (UTC)

No, honestly. You want to meet at Saturday, 4PM UTC (or whatever european time zone)? Get the latest Dow opening before Saturday, 4PM you-local-time. Just works.

Using the value available at the time of the calculation looks the way to go

Is the DOW/timezone thing a problem for Saturday meetups in Europe? Saturday's coordinates are generated from Friday's DOW opening value, which is available at 0930 EDT (1430 BST in the UK) on the Friday. So there's over 24 hours notice for the meetup coordinates in Europe. - Ytaya

md5 Collisions?

What about collisions in the md5 algorithm?

What about them? In theory, two dates/stock market prices might end up with the same meetup point. Unlikely, and probably not a terribly big deal? Zigdon 07:39, 21 May 2008 (UTC)

There are situations where cryptographic collisions are a problem, but this isn't one of them. md5 is just being used as a pseudorandom number generator here, and it has a very small-entropy seed (someone call Debian!). So its cryptographic strenth isn't particularly relevant. --Xkcd 07:43, 21 May 2008 (UTC)xkcd

Nearby Points?

I forgot to mention that the algorithm doesn't necessarily find the point closest to your present location. Ofcourse, the user can manually select the other regions around his location to find the closest meeting point, but it would be nice if the google earth app would show the 4 closest locations. That way, the chance of meeting different people is greater, because any user would be in 9 regions instead of just one. This could also be useful if the closest point in unreachable, where the user could choose to go to the next closest meeting point. - Sparky

Well, it depends ... generally you'll have one population center surrounded by fairly empty areas. I think we'll be able to better answer this question after a week's experience. --Xkcd 07:46, 21 May 2008 (UTC)xkcd

That, also, depends on where you live. The distance between two closest points horizontally or vertically is approximately 111km. The Netherlands is barely 200km wide. Especially in the western part of the country, which is the most densely populated, cities are rarely more than 15km apart. - Sparky

This is most excellent, I know I'm participating! -Sir_Lewk

Would it be possible to include the route-planning feature in the map? For those without navigation systems, that would be very useful. - Sparky.

I'm from Australia, is there any chance of this being implemented in the Pacific Region as well? It sounds like a great idea. - Zorg

Two thoughts for improvements:

• Maybe use a smaller step size ? If you do not own a car then the destination can be unreachable. Also in Europe (where i am) the polpulation density is in general higher, so one grid cell might encompass two major cities.

We discussed this quite a bit -- currently, the average driving distance is something like 45-50 miles. But if you're trying to have an xkcd meetup for your city, it'd only compound the problem of cities being split up. Half your friends would go to one and half to another. It's already bad enough in DC and Chicago. --Xkcd 09:12, 21 May 2008 (UTC)xkcd

This, ofcourse, strongly depends on the population density (or actually, the XKCD reader density). If you make the regions smaller, the chance of 2 or more people meeting there decreases. As people fail to meet, they stop trying, further reducing the change of a successful meeting for those who try at a later date. - Sparky.

And L.A., Pittsburgh, Philadelphia, Denver... - Cahlroisse

• 45-50 miles is too much for nonprofessional cyclists, are we encouraging petrol burning? Too bad for the ecosystem :P 80.36.82.38 10:01, 21 May 2008 (UTC)

• I think the algorithm should include the base coordinates (the integer portion of your gps location, or maybe even some secret number?) in the hash, otherwise the meetup points form a regular grid, offset by a fixed value from the base coordinates. - Mucki

I don't really see why that's a problem. In fact, it has a couple benefits -- if one coord is all the way to the north of a graticule and you're at the south end, it means the coord in the graticule to the south will be close to you. --Xkcd 09:12, 21 May 2008 (UTC)xkcd

I'd agree; I don't see what's wrong with a regular grid of possible meeting locations, while the upside is that the nearest location is at most 1.4 * 111 / 2 = 78.5km away (half the diagonal of a 111 * 111 square), assuming it is reachable, ofcourse. - Sparky.

Oddly, where I live (Boreham, Chelmsford, Essex, UK), apparently whatever day it is, I should be meeting in the exact same place in the Thames estuary (I've tried about 5 different dates). Is there something amiss?91.107.26.104

It seems to be working fine. Different coordinate for every day this past week in the 51, 0 (east) graticule that contains Chelmsford. Any more details on the problem? --Xkcd 09:24, 21 May 2008 (UTC)xkcd

hi there, about one thid of my sector is covered with water. are you going to do any sea/ocean detection?

This may have been covered already, but i'm confused about how the center of mass calculation is working. No doubt a cost function of some kind, but the question is why land mass isn't taken into account, or so it would seem! For example: where i am (Southampton, Hampshire, UK) the center of pass seems to be somewhere in the ocean. Now i realise this is probably due to the isle of white right below southampton. Possible solution, if the area covered by the center of pass holds more than...i don't know...40% water, adjust some variable to force a reduction in granularity. Mainly because the geohashes for the past 4 days have been in the middle of the sea and the reason is clearly just the odds given the amount of water in southampton's center of mass. Also, i've got a python implementation of this appy going, but i don't have access to the center of masses, though this might be me just being silly. Are these available somewhere in a handy dandy XML format?, cheers - Sina

The squares are the zones bounded by latitude and longitude lines, nothing more. This means the configurations are sub-optimal for some cities, and there will be various conventions for dealing with those.

Oh i see! Talk about over complicating things in my mind :). And the lat/long for each square is the center of the square i assume? or what? Also is it cool if i use the dow data avaiable at http://irc.peeron.com/xkcd/map/data/ for my python implementation directly? or should i contact another webservice somewheres? SinJax