title: Creating a brushable map with vega-lite API
body: <p>I am trying to create an interactive map in vega-lite API that allows selecting multiple points on the map. Selecting a single point works with vl.selectPoint(), but when I change to vl.selectInterval() which is the behavior I want, I get the following error message:</p>
  <pre><code>Error: Expression parse error:  ? name1_scale_trigger : {}
  </code></pre>
  <p>I put the code illustrating the problem in an <a href="https://observablehq.com/@emanueles/testing-an-interactive-map-in-vega-lite" rel="nofollow noreferrer">observablehq notebook</a>.</p>
  <p>Any help on how to get it working is very appreciated.</p>
  <p>Thanks!</p>