explain xkcd - User contributions [en]

1196: Subways

2015-12-23T19:16:52Z

162.158.60.5: /* New York City */

{{comic
| number = 1196
| date = April 8, 2013
| title = Subways
| image = subways.png
| titletext = About one in three North American subway stops are in NYC.
}}
*The xkcd page links to [http://xkcd.com/1196/large/ a much larger version], which has another text added:
<blockquote style="font-style:italic">
For the pedantic rail enthusiasts, the definition of a subway used here is, with some caveats, "a network containing high capacity grade-separated passenger rail transit lines which run frequently, serve an urban core, and are underground or elevated for at least part of their downtown route." For the rest of you, the definition is "a bunch of trains under a city."
</blockquote>
{{TOC}}

==Explanation==
[[File:North American subways.svg.png|right|border|link=http://www.radicalcartography.net/subways.html|North America Subways by Prof. Bill Rankin]]
The comic shows the maps of all North American {{w|subway}} networks. In reality, none of these systems are interconnected, but in the diagram subways from different cities that have the same color on the official subway map have whimsically named connections, such as the "Ohio-California Tunnel" connecting the Green Lines of Cleveland and Los Angeles, or the "Rocky Mountain Tunnel" connecting the Blue Lines of Chicago and San Francisco. Vancouver and San Francisco are connected through a station called Richmond, which appears to double as {{w|Richmond, British Columbia}} and {{w|Richmond, California}}. The "Springfield Monorail" is fictional, from the animated series ''{{w|The Simpsons}}'' (see {{w|Marge vs. the Monorail}}), but its approximate location on this map would suggest the [http://www.seattlemonorail.com/ Seattle Monorail], or perhaps Springfield, Oregon, which [http://www.smithsonianmag.com/arts-culture/Matt-Groening-Reveals-the-Location-of-the-Real-Springfield.html Matt Groening revealed was the inspiration for the Simpsons' hometown].

The [http://www.radicalcartography.net/subways.html Urban Mass Transit Systems of North America] map (right) created by [http://hshm.yale.edu/rankin Yale Professor Bill Rankin] on his web site [http://www.radicalcartography.net/ Radical Cartography] in 2006 presents all of the subway systems in North America at the same scale using geographic, instead of topological, layout.

The networks on xkcd's map are displayed in (relatively) geographic position, with {{w|Vancouver}} being the most North-West, and {{w|Mexico City}} being the most South – East/West and North/South order are correct, but distances are not (in reality, Vancouver is closer to Chicago than to Toronto for example). The map's design is modeled after the system map of the {{w|Massachusetts Bay Transportation Authority}} in Boston where Randall is from.

===City-specific notes===

====Vancouver====
*The {{w|Canada Line}} and the {{w|Expo Line (TransLink)|Expo Line}} are shown as the same color; SkyTrain's official maps depict them with light blue and dark blue respectively.
*{{w|Richmond, British Columbia|Richmond}} is the name of the city where the southernmost terminus of the Canada Line is located, and shares its name with {{w|Richmond, California}} (see San Francisco section.)

====Boston====
*The "Green Line Extension to Canada" references {{w|Green Line Extension|the actual project}} to extend the {{w|Green Line (MBTA)|Green Line}} into Medford, north of Boston.
*The "Ashmont–Manhattan High-Speed Line" shown as connecting Boston's Red Line to New York City's 1 train is a play on the {{w|Ashmont-Mattapan High Speed Line}} in Boston.
*The {{w|Red Line (MBTA)|Red Line}} stops "Skinflower" and "Bonevine" are plays on the actual name of the Red Line's terminus, {{w|Braintree (MBTstation)|Braintree}}.

====San Francisco====
*Both Muni and BART are depicted in San Francisco's map and are completely separate systems, although the map gives the impression that trains interline between the two. Non-wheelchair-accessible stops on Muni lines are omitted.
*{{w|Richmond, California|Richmond}} is the name of the city where the northern terminus of the {{w|Richmond-Fremont line|Richmond–Fremont}} and the {{w|Richmond-Daly City/Millbrae line|Richmond–Daly City/Millbrae}} BART lines are located, and shares its name with {{w|Richmond, British Columbia|Richmond, British Columbia}} (see Vancouver section.)
*"Sunnydale" is the {{w|Sunnydale Station|actual name}} of the terminus of the Muni {{w|T Third Street}} line, not to be confused with {{w|Sunnydale|the city}} where ''Buffy the Vampire Slayer'' is set.

====Los Angeles====
*The {{w|Gold Line (Los Angeles Metro)|Gold Line}} and the {{w|Orange Line (Los Angeles Metro)|Orange Line}} are shown with swapped colors.
*The Orange Line is the only {{w|bus rapid transit}} (BRT) line to be shown on the map. LA Metro also operates a second BRT line, the {{w|Silver Line (Los Angeles Metro)|Silver Line}}, which is not shown.

====New York City====
*The {{w|New York City Subway}}, {{w|Port Authority Trans-Hudson}} (PATH), and the single line of the {{w|Staten Island Railway}} (with a connection via the {{w|Staten Island Ferry}}) are shown.
*{{w|Jamaica, Queens|Jamaica}} is the name of the neighborhood in Queens where the E, F, and J/Z trains terminate. Kingston is the capital and largest city in the country of Jamaica.
*The actual {{w|G (New York City Subway service)|G train}} is notorious for unreliable service, hence the "Random Service" notation.
*The "Robert Moses High-Speed Line" refers to the NYC urban planner {{w|Robert Moses}}, who was one of the most influential planners in supporting cars over all public transport, creating the car-dependent {{w|New York metropolitan area}}.

====Philadelphia====
*Both {{w|SEPTA}} subway lines, a portion of the {{w|SEPTA Subway–Surface Trolley Lines}}, and the {{w|PATCO Speedline}} are shown.
*"Trolley Rt. 10 to California" is a play on the actual {{w|SEPTA Route 10|Route 10}} trolley.

====Washington, DC====
*The "Graveyard for passengers killed by closing doors" refers to the warning played in the Washington DC Metro system advising passengers that the subway doors are "not like elevator doors" and will close on your limbs or belongings rather than opening when contact with an object is detected.
*The "Morgantown, WV Automated Line" references the {{w|Morgantown Personal Rapid Transit}} system, which was built in 1975 as a {{w|personal rapid transit}} demonstrator and serves the three campuses of West Virginia University.
*{{w|Greenbelt (WMATA station)|Greenbelt}} is the northern terminus of the Washington Metro's Green and Yellow lines, hence the Green line being depicted as forming a belt.

====Miami====
*The "Caribbean Metromover" references the {{w|Miami Metromover}}, a people mover in downtown Miami (not shown on the map.)
*The airport logo for Miami International Airport (MIA) is replaced with a [http://www.youtube.com/watch?v=ewRjZoRtu0Y paper airplane].

====San Juan====
*The "Puerto Rico Submarine" that connects the Red Lines of San Juan and New York refers to the fact that San Juan is on an island, namely {{w|Puerto Rico}}.
*The "Mona Tunnel" that connects the Red Lines of San Juan and Santo Domingo may refer to the island of {{w|Isla de Mona|Mona}}, which lies between Puerto Rico and Hispaniola.

====Monterrey====
*The "Chicxulub Tunnel" that connects the Red Lines of Santo Domingo and Monterey refers to the 65-million-year-old {{w|Chicxulub crater}}, which lies roughly between the two cities.

===Official subway maps===
*Atlanta - http://www.itsmarta.com/rail-schedules-or-route.aspx
*Baltimore (MTA Maryland) - http://mta.maryland.gov/sites/default/files/metro-subway.jpg
*Boston - http://www.mbta.com/schedules_and_maps/subway/
*Chicago (CTA) - http://www.transitchicago.com/assets/1/maps/P19_2012_CTA_Rail_Map.pdf
*Cleveland - http://www.riderta.com/pdf/maps/System_Map_Rapid_Connect.pdf
*Los Angeles (LACMTA) - http://www.metro.net/riding_metro/maps/images/rail_map.gif
*Mexico City - http://www.metro.df.gob.mx/imagenes/red/redinternet.pdf
*Montreal - http://www.stm.info/english/metro/images/plan-metro.jpg
*New York City (MTA) - http://www.mta.info/maps/submap.html
*New York City (PATH) - http://www.panynj.gov/path/maps.html
*Philadelphia (SEPTA and PATCO) - http://www.septa.org/maps/system/index.html
*San Francisco (BART) - http://www.bart.gov/images/global/system-map.gif
*San Francisco (MUNI) - http://transit.511.org/static/providers/maps/SF_712200722845.gif
*Toronto (TTC) - http://tourbytransit.com/toronto/images/Toronto-Subway-Map.png
*Vancouver - http://mapa-metro.com/mapas/Vancouver/mapa-metro-vancouver.png
*Washington (WMATA) - http://wmata.com/rail/maps/map.cfm

{{clear}}

==Transcript==
:'''Subways of North America'''
:[A subway-line style (bold colored, 45-degree aligned lines with white bars indicating stations) map has been constructed by combining and linking various parts of the subway maps from many different cities, as if all of the transit systems were connected directly. The cities include (from top to bottom, left to right) Vancouver, Montreal, San Francisco, Toronto, Boston, Chicago, Los Angeles, Cleveland, New York City, Philadelphia, Baltimore, Washington DC, Miami, Atlanta, Monterrey, San Juan, Santo Domingo, and Mexico City.]

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Charts]]
[[Category:Large drawings]]

Talk:1597: Git

2015-12-21T20:35:21Z

162.158.60.5:

If someone is interested, the best book I've read on it is [http://www.git-scm.com/book/en/v2 Pro Git]. The chapters 2 and 3 explain pretty well this mess of branching and merging. But it's true that it takes a bit of patience to go over it all. [[Special:Contributions/108.162.228.35|108.162.228.35]] 08:47, 30 October 2015 (UTC)

Also take a look at [http://nvie.com/posts/a-successful-git-branching-model/ GitFlow: A Successful Git Branching Model]. Though Randall is correct there usually comes a time when it is easier to give up and "start again". [[Special:Contributions/162.158.34.147|162.158.34.147]] 08:53, 30 October 2015 (UTC)

I never liked the name of this piece of software; in British English, the name "git" is mildly rude :-)
https://en.wikipedia.org/wiki/Git_(slang) . [[User:Gearoid|Gearóid]] ([[User talk:Gearoid|talk]]) 09:20, 30 October 2015 (UTC)
:According to word of god it was on purpose: https://en.wikipedia.org/wiki/Git_(software)#History [[Special:Contributions/162.158.22.46|162.158.22.46]] 11:41, 30 October 2015 (UTC)
:He also designed it in such a way that people often run into problems with commitment to detached heads, and typically deal with this by reflogging... {{unsigned ip|108.162.249.161}}

'Internally, Git works by saving the differences between various versions of the files, rather than creating a new copy each time the user "commits" the current version of the code.' - It is exactly the opposite. It stores whole files, or rather all committed pieces of data (blobs). See http://gitready.com/beginner/2009/02/17/how-git-stores-your-data.html [[Special:Contributions/141.101.88.202|141.101.88.202]] 09:38, 30 October 2015 (UTC)TK

: It is stored as diffs in pack file. Whole file (loose object) are packed automatically by default.
:
: See https://schacon.github.io/gitbook/7_the_packfile.html and https://www.kernel.org/pub/software/scm/git/docs/git-pack-objects.html
[[Special:Contributions/162.158.177.59|162.158.177.59]] 10:15, 30 October 2015 (UTC)

::Not sure what pack files are used for, but data is stored as is and named by the SHA-1 of its contents. See [https://schacon.github.io/gitbook/1_the_git_object_model.html object model] in the same reference. [[User:Walenc|Walenc]] ([[User talk:Walenc|talk]]) 16:02, 30 October 2015 (UTC)

I think you guys need to differentiate between the underlying data scheme, and the command line. The way git stores underlying data is indeed beautiful, but the command-line is the worst UI ever. You know how you switch to working on a different branch? "git checkout". You know how you revert the changes you've made to a file? "git checkout". You know how you make a new branch? "git checkout -b". If you're used to other systems, you'll find nearly every operations - even common ones - counterintuitively named. I work at Google and even here, every week someone near me screws up their respository enough that they have to save their work, nuke their repo, reapply their changes, and try moving forward again. I don't know why anyone puts up with this! (Actually I do - it's because if you're collaborating between companies, git does it better than anything else.) [[Special:Contributions/199.27.129.107|199.27.129.107]] 18:46, 2 November 2015 (UTC)

: That's not actually true. git checkout takes you to a node of development, as a convenience that can be either the entire code base (a branch) or a single file. You could remove the file you want to 'revert', stash all other changes, checkout HEAD and then pop the stash...or use the git checkout FILE shortcut. git checkout -b is just a shortcut so you don't have to do git branch; git checkout. [[Special:Contributions/108.162.220.239|108.162.220.239]] 06:00, 7 November 2015 (UTC)

I feel like this article should end with a quick guide to git commands. {{unsigned ip|108.162.216.27}}

Well, I feel this article focuses on explaning git too much that it loses the point of the joke. We have Wikipedia to refer readers to ... The thing is, not just users who are unable to use git beyond a few basic commands, but also those who understand git often use some sort of "start over" method because an action looking perfectly legit got the repository into unusable state, where recovery is much more difficult than reapplying patches. For one of the most common, search for "detached head", for example - especially funny when git insists on falling into that state after checking out master which is in direct contradiction to what docs say when it happens. But I don't feel like rewriting that, sorry :-/ --kavol, [[Special:Contributions/141.101.96.206|141.101.96.206]] 16:04, 30 October 2015 (UTC)

I feel you've all been nerd-sniped. [[Special:Contributions/108.162.216.8|108.162.216.8]] 19:33, 30 October 2015 (UTC)Pat

The problem is not about the working copy and about the branching tree structure and some git internals that is quite confusing.
This 4 years old reddit post can be used as a funny reference: https://www.reddit.com/r/programming/comments/embdf/git_complicated_of_course_not_commits_map_to/

http://tartley.com/?p=1267
"One of the things that tripped me up as a novice user was the way Git handles branches. Unlike more primitive version control systems, git repositories are not linear, they support branching, and are thus best visualised as trees, upon the nodes of which your current commit may add new leaf nodes. To visualise this, it’s simplest to think of the state of your repository as a point in a high-dimensional ‘code-space’, in which branches are represented as n-dimensional membranes, mapping the spatial loci of successive commits onto the projected manifold of each cloned repository." {{unsigned ip|108.162.210.212}}

Should someone mention how git is by default used through a terminal - which is often more confusing than a GUI for most people - and that while there are graphical shells for git, some people refuse to use them because they're not fully-featured? [[Special:Contributions/108.162.221.36|108.162.221.36]] 11:43, 30 October 2015 (UTC)

The really sad part of all this is that if you work in a multi-dev environment and anyone on the team is doing what Cueball suggests, it negates every other user's ability to use the main trunk properly. [[User:Ericm301|Ericm301]] ([[User talk:Ericm301|talk]]) 02:26, 31 October 2015 (UTC)

Hasn't it got too extensive about git? I've never used git but quite understood the comedy. I just visited this page to know about git.txt and there's nothing about it but just long text that doesn't help whatsoever to understand the comic. [[Special:Contributions/141.101.84.125|141.101.84.125]] 08:45, 31 October 2015 (UTC)

:I agree completely! I've stripped out the overlong discussion of git's features. --[[User:Slashme|Slashme]] ([[User talk:Slashme|talk]]) 00:12, 1 November 2015 (UTC)

AFAIK, the git.txt is not the part of the Git itself. I just added it to explanation. [[Special:Contributions/162.158.114.231|162.158.114.231]] 20:21, 31 October 2015 (UTC)

:"This comic is a play on how git, a popular version control system, is misused by people who have a very poor understanding of its inner workings."

Comically missing the point. That is NOT what the comic is about, that is a poor excuse from a fanboy. --[[Special:Contributions/162.158.90.159|162.158.90.159]] 12:00, 1 November 2015 (UTC)
: I agree the verbose "explanation" misses the point. The reality is that git is a confusing mess from a user's point of view. It's a very nice and powerful design from a technical point of view yet one that will mostly confuse anyone who encounters it at first; most people are afraid of admitting it because they don't want to look dumb. There's beauty in a design that is user-friendly at its core, and git misses that mark. [[User:Ralfoide|Ralfoide]] ([[User talk:Ralfoide|talk]]) 17:38, 1 November 2015 (UTC)

: The same can be said of Linux. It seems to be a common theme in Linus Torvalds' work. [[Special:Contributions/108.162.249.163|108.162.249.163]] 23:52, 1 November 2015 (UTC)

In pretty much every team I've worked I found there ends up being one "git expert" that raises above the rest and people continuously go see that person with "I don't know how to do X", to which the expert will often reply with a magic unheard-of-before git command line that looks pretty much like perl line noise. [[User:Ralfoide|Ralfoide]] ([[User talk:Ralfoide|talk]]) 17:38, 1 November 2015 (UTC)

In what world are telephones not an electronic mean of communication ? [[Special:Contributions/141.101.75.245|141.101.75.245]] 10:56, 2 November 2015 (UTC)

That's not the point. The distinction was being made (ambiguously, perhaps) between electronic and vocal communication. We might naturally turn to telephones for the latter.--[[Special:Contributions/162.158.2.227|162.158.2.227]] 12:16, 2 November 2015 (UTC)

ExplainXKCD is usually amazing, but the explanation above is really "comically missing the point".

:Git has a very cool distributed architecture, but the user experience is much more complex than other revision control systems. TFS and subversion can be taught to junior developers in about 20 minutes, but it takes much longer to learn how to use Git’s basic features. It is very easy for Git to become deadlocked, which requires some obscure commands to fix. Unless you are an expert at Git, it is sometimes easier to delete your project and try again.

:There are things that Git does that other RCS don’t do. (I am not entirely sure what they are, to be totally honest. When the question is asked, the responses usually just talk about the architecture.) Git experts tend to like that the software is more powerful than other RCS systems, and some tend to be dismissive of how difficult other people find it to use. Many people (such as myself and Cueball) find the architecture cool, but are not Git experts.

:So this is the joke. There is a conflict between how experts typically TALK about Git, and how most users actually USE Git. The humor comes from having a character say things that many people think, but wouldn’t say out loud for fear of looking stupid.

Would it be worth polishing the above and adding it to the description, or would that just be flamebait?
[[Special:Contributions/108.162.246.86|108.162.246.86]] 16:08, 2 November 2015 (UTC)

The title text may be referring to the famous saying: "Git is really pretty simple, just think of branches as homeomorphic endofunctors mapping submanifolds of a Hilbert space." [[Special:Contributions/162.158.255.40|162.158.255.40]] 23:23, 2 November 2015 (UTC)

The current explanation is wrong [not anymore, it's excellent now!]. As others have stated, the comic is clearly making fun of git itself, NOT of its users. [[User:Daskas|Daskas]] ([[User talk:Daskas|talk]]) 13:44, 3 November 2015 (UTC)

Wow, it's amazing how there are comments above defending git: those commentators lost the fact that XDCD is making fun of git because of it's idealistic view of source control doesn't map at all to reality, which in many cases, leads to user frustration and... dare I say it, lost data and lost productivity. Git is a joke and XKCD highlighted that well :) [[Special:Contributions/162.158.60.5|162.158.60.5]] 20:35, 21 December 2015 (UTC)

816: Applied Math

2015-11-18T21:27:11Z

162.158.60.5:

{{comic
| number = 816
| date = November 8, 2010
| title = Applied Math
| image = applied_math.png
| titletext = Dear Reader: Enclosed is a check for ninety-eight cents. Using your work, I have proven that this equals the amount you requested.
}}

==Explanation==
{{w|Donald Knuth}} is a {{w|computer scientist}} who has written several computer science textbooks and he offers {{w|Knuth reward check|monetary rewards}} for anyone finding errors in his publications. The first error found in each book is worth US$2.56. Other suggestions are worth less than $2.56, but a check is still sent out if Dr. Knuth finds them to be reasonable.

[[Megan]] uses a proof to invalidate logic itself. According to the logic symbols [[File:contradiction.png]] at the bottom of the proof, she has proved that "the proposition (statement) is true and the proposition is false," i.e. "something is both true and false." (Specifically, ∴ means "therefore", ''P'' represents that a proposition is true, ∧ stands for "and", and an overbar negates a proposition (so ''P'' represents that a proposition is false)). If someone were to prove this, it would indeed derail the very foundation of logic and result in the {{w|principle of explosion}}, which is referenced in [[704: Principle of Explosion|a previous comic]].

Since most of the content of computer science textbooks is fundamentally based on logic, Megan's proof obviously spells doom for Dr. Knuth's, as each instance of logic can now be considered an error. After Megan's friend confirms the validity of her proof, Megan writes a letter to Dr. Knuth to collect her money for the 1,317,408 errors in {{w|The Art of Computer Programming}} at $2.56 each. Note that using Megan's work, any number of errors, including zero, is both equal and unequal to 1,317,408 errors, and she chose the number 1,317,408 arbitrarily.

The title text is the reply from Dr. Knuth, in which he uses Megan's logic-disproving proof against her by claiming — with no logical explanation — that the amount of money she is in fact due as a reward is only 98 cents. He does this presumably to a) get out of paying her over three million dollars, b) demonstrate his contempt for or disbelief in her proof, and/or c) to show her, rather passive-aggressively, that she herself is not exempt from any ill effects resulting from her ridiculous proof. If logic is proved to be false, then all mathematics are proved false and 3,372,564.48 = 0.98.

The title of the comic, "Applied Math," is a play on {{w|Applied mathematics}}, "mathematical methods that are typically used in science, engineering, business, and industry," as opposed to {{w|pure math}}, which focuses exclusively on abstract concepts. Instead of using math to calculate something like the speed of a falling object, Megan uses it for an ostensibly more frivolous reason: to gain a huge reward via a proof of dubious validity.

==Transcript==
:[Ponytail is standing at a whiteboard considering a logical proof. The proof assumes ''P'' and deduces ''P'' ∧ ''P''.]
:Ponytail: Wow. I can't find fault with your proof.

:[Ponytail is still looking at the white board, the frame expands to show Megan walking away, rubbing her hands together in an evil manner.]
:Ponytail: You've show the inconsistency — and thus the invalidity — of basic logic itself.
:Megan: Excellent. On to step two...

:[Megan sits down at a desk and begins to write.]
:Dear Dr. Knuth,

:[She continues to write.]
:I am writing to collect from you the $3,372,564.48 I am owed for discovering 1,317,408 errors in ''The Art of Computer Programming...''

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Donald Knuth]]
[[Category:Logic]]