title: Handle URL Parameters with Gatsby
body: <p>I'm using React &amp; Gatsby to create a website and I've got everything laid out the way I want, I'm just having some problems understanding how to use URL Route parameters to change content that is displayed. </p>
  
  <p>For example, say I have a page <code>categories.js</code> which listens to <code>http://website.com/categories</code> but I want to be able to dynamically handle any URL parameters like such:</p>
  
  <p><code>http://website.com/categories/animals</code> </p>
  
  <p>When using <code>gatsby-link</code> like so: <code>&lt;Link to="/categories/animals" /&gt;</code> it wants me to create a file called <code>animals.js</code> in a categories folder. Instead, I want categories.js to be able to handle the rendering for this page and select the content appropriate based on the category passed in the URL parameters. </p>
  
  <p>Other than the items displayed, this page is exactly the same through all categories, so it doesn't make sense for every category to have it's own static page. </p>