Explain xkcd: It's 'cause you're dumb.
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File names often end in file extensions like ".ppt" or ".exe", used to determine the type of content contained in the file. Generally (but not always), a particular extension will only be used by a specific program or small set of programs, making a file's extension a quick indicator of how the file might have been produced.
Because of that last part, and the fact that certain programs will tend to be used by only certain types of people, Randall suggests here that a file's extension may provide a hint toward how trustworthy the file's content may be.
- .tex files are source files for the programs TeX and LaTeX, which are used often and almost exclusively by academics, especially in mathematics and the hard sciences. .tex pretty much means serious business.
- .pdf files are a document format by Adobe, frequently used for publication. Thus, a .pdf file is likely to be some type of final product or polished work.
- .csv files contain a bunch of raw data delimited by commas, and are likely computer-generated (from, say, a scientific experiment).
- .txt files contain only plain text, no "rich text" or anything fancy. Programmers use them for README files.
- .svg files are a vector graphics format used a lot for diagrams, such as on Wikipedia.
- .xls and .xlsx files are spreadsheets used and created by the program Microsoft Excel, part of a bundle of applications known as Microsoft Office (also supported by compatible free software such as LibreOffice). These applications are very commonly used, especially for business, finance and data analysis tasks. .xls is used for Excel versions prior to 2007, while .xlsx is used for Excel versions 2007 and later.
- .doc files are a rich-text document format used and created by the program Microsoft Word, another application in the Microsoft Office bundle. As with .xls, almost anyone with access to Microsoft Office could easily make one of these. Unlike Excel, Word is pretty much the #1 textual file format, which is presumably why Randall doesn't trust it much.
- .png files are a bitmap image format designed for the Internet. They enjoy wide popularity for providing crisp, full-color images with lossless (invisible) compression. Almost all xkcd comics, this diagram included, use PNG. But since he rates the format so low, is Randall saying we shouldn't trust this chart?
- .ppt files are used and created by the program Microsoft PowerPoint; as with the other two Office applications, almost anyone could easily make one of these. As they are usually used for presentations rather than documents, the information in them may be arranged differently, possibly to "dumb down" the content, or in marketing materials or talks in which the author may not be very objective.
- .jpg files are another image format with high compression capabilities, good for storing photos, and not so good for many other things. JPEG is prone to annoying compression artifacts, so it's generally bad for images of numerical or textual information. Cameras often take high-quality photos in the .raw format and then compress it into a much, much smaller JPEG; a JPEG file's content may be less trustworthy as it doesn't contain as much of the detail in the original image.
- .jpeg files are the same thing as .jpg files; however, it is more likely that an image with this extension was created manually rather than automatically by, for example, the aforementioned digital camera. This makes it less trustworthy.
- .gif files are yet another bitmap image format, notable for supporting short animations. GIF was once the Internet image file format until PNG gradually replaced it. Since GIF is the only common image format capable of animation, it is often used to contain things like silly clips of cats falling into boxes, or blinking advertisements claiming that you're the 570,000th VISITOR!. Their frequent use in the most annoying types of advertisements (pop-ups, etc.) is presumably why Randall deems it the least trustworthy out of all file extensions listed here. Additionally, GIF files can be concatenated with a ZIP file to hide an archive within a GIF file (Steganography), thus resulting in a file that can easily be untrustworthy.
Note that while the extensions .xls/.xlsx, .doc, and .ppt were originally exclusive only to Microsoft Office and users of Windows, there now exist a number of open source programs such as Open Office, Libre Office, and some Android apps that are capable of editing such files. These programs can run on systems other than just Windows, such as Linux, perhaps contributing to making them even more widespread and easy to make than before.
The title text refers to how .txt files contain only plain text and nothing else, meaning that any alignment (such as for indentation or tables) would have to be performed manually by adding in spaces or tabs. Anyone who would go through such an effort to improve their text's readability is likely to be trustworthy.
- Trustworthiness of Information by File Extension
- [A bar graph charting this. No units or figures are given, but for ease of comprehension this transcript will arbitrarily designate the highest score as "+100"; subsequent scores are estimates based on the size of their bars.]
- .tex: +100
- .pdf: +89
- .csv: +85
- .txt: +67
- .svg: +65
- .xls/.xlsx: +49
- .doc: +21
- .png: +15
- .ppt: +14
- .jpg: +3
- .jpeg: -8
- .gif: -36
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