Refer to zoom level in TileMill expressions

Question

Is it possible to do something like this:

#ways[highway="trunk"] {
  line-color:#c99;
  line-width:@zoom/10;
}

Obviously that example doesn't work. Is there another way to do arithmetic expressions involving the zoom level?

Answer 1

You can't use zoom as a variable at the moment as you mentioned. I've read this is planned (and I'm excited to see it implemented too).

Here's one work-around, etc:

  #ways[highway="trunk"] {
  line-color: #c99; 
  [zoom=10] { line-width: 1; }
  [zoom=11] { line-width: 1.1; }
  [zoom=12] { line-width: 1.2; }

---

If you have multiple highway types, you could also do:

@z10base=10;
@z11base=11;

  #ways[highway=trunk"] {
  line-color: #c99; 
  [zoom=10] { line-width: @z10base; }
  [zoom=11] { line-width: @z11base; }
  }

 #ways[highway="primary"] {
  line-color: #000000; 
  [zoom=10] { line-width: @z10base + 4; }
  [zoom=11] { line-width: @z11base + 8; }
  }