add_fill_layer</a></span><span class="op">(</span></span></span>
<span class="r-in"><span>        id <span class="op">=</span> <span class="st">"Census tracts"</span>,</span></span>
<span class="r-in"><span>        source <span class="op">=</span> <span class="va">tr</span>,</span></span>
<span class="r-in"><span>        fill_color <span class="op">=</span> <span class="st">"purple"</span>,</span></span>
<span class="r-in"><span>        fill_opacity <span class="op">=</span> <span class="fl">0.6</span></spa