Snip!t from collection of Alan Dix

<p class="introduction" id="story_continues_1">A study of the world's largest subway networks has revealed that they are remarkably mathematically similar.</p> <p>The layouts seem to converge over time to a similar structure regardless of where or over how long they were built. </p> <p>The study, <a href="http://rsif.royalsocietypublishing.org/lookup/doi/10.1098/rsif.2012.0259">in the Journal of the Royal Society Interface</a>, analysed 14 subway networks around the world.</p> <p>It found common distributions of stations within the networks, as well as common proportions of the numbers of lines, stations, and total distances.</p>