Conditional styling and expressions using modulus

Question

I'm trying to style a contour shapefile in TileMill with all contour lines divisible by 100 bolder than others. Can I use expressions in defining a condition? The following example of course does not work, but it gives an idea of what I am trying to get.

#contours {
  line-width:.4;
  line-color:#222222;

  [(elev % 100 = 0)]{
    line-width: 1;
    line-color: #000;
  }

}

Answer 1

I achieved this by creating a second shapefile which only contained the n th contour (100 in your example), but it would be preferable to style a single shapefile in the way you describe.

Answer 2

TileMill doesn't support the modulus operator in expressions. So, your options are either to pre-process the shapefile, which can be annoying, or to import the data from a PostGIS database and define an 'elev%100' column on the fly.