title: System(s) for encoding data using a limited set of characters
body: <p><strong>up-front clarification of exactly what I need:</strong> I would like to know - <em>are there any standards or conventions for encoding information like this within a url that I might try to use to read what it says</em>? </p>
  
  <p>I'm sure there are established methods for encoding binary information using non-binary character sets. In this case each location can be occupied by one of 66 different characters, so each "byte" is slightly longer than six bits if you look at it logarithmically. </p>
  
  <p>For example, a link in a mail message I received from the IEEE was surprisingly long:</p>
  
  <blockquote>
    <p><s>http://</s>links.mail.spectrum.ieee.org/mpss/c/4wA/vCMaAA/t.1xp/MW0ThjonTUa...
    ...6Bg3tXEzxb1xlZ4zyB3umN-2BxkLQw6LtGSGH3ghSDqpqiUmxfSVUprd0HnHYipmddjyE-3D</p>
  </blockquote>
  
  <p>876 characters in toto (I've deleted most of it here) - over half a <em>kilobyte</em>!</p>
  
  <p>The encoding must conform to legal characters within a url, the coding in the url I received uses 66 ASCII characters only - see below.</p>
  
  <p>Probably - of course - it is proprietary and there's little hope, but I'd like to know if there do exist some standards that allow these to be readable if so desired.</p>
  
  <p>My math:</p>
  
  <pre><code>841 * (log(26+26+10+4) / log(2)) / 8 / 1024
  </code></pre>
  
  <p>~0.62 kb</p>
  
  <p>26 uppers, 26 lowers, 10 digits and 4 punctuation characters for this estimate. <code>['-', '/', '.', '_']</code></p>
  
  <p>Since urls have a <a href="https://stackoverflow.com/a/417184/3904031">de facto limit of 2000 characters</a>, a crafted url can carry over a kilobyte of "individualized" information.</p>