Language Elements

Below is a list of values and an explanation of any expression that can be applied to properties in CartoCSS.

Color

CartoCSS accepts a variety of syntaxes for colors - HTML-style hex values, rgb, rgba, hsl, hsla, hsluv, and hsluva. It also supports the predefined HTML colors names, like yellow and blue.

#line {
  line-color: #ff0;
  line-color: #ffff00;
  line-color: rgb(255, 255, 0);
  line-color: rgba(255, 255, 0, 1);
  line-color: hsl(100, 50%, 50%);
  line-color: hsla(100, 50%, 50%, 1);
  line-color: hsluv(100, 50%, 50%); // same values yield different color than HSL
  line-color: hsluva(100, 50%, 50%, 1);
  line-color: yellow;
}

Especially of note is the support for HSL and HSLuv, which can be easier to reason about than RGB. CartoCSS also includes several color operation functions borrowed from LessCSS:

// lighten and darken colors
lighten(#ace, 10%);
darken(#ace, 10%);

// saturate and desaturate
saturate(#550000, 10%);
desaturate(#00ff00, 10%);

// increase or decrease the opacity of a color
fadein(#fafafa, 10%);
fadeout(#fefefe, 14%);

// spin rotates a color around the color wheel by degrees
spin(#ff00ff, 10);

// mix generates a color in between two other colors.
mix(#fff, #000, 50%);

// get color components
hue(#ff00ff);
saturation(#ff00ff);
lightness(#ff00ff);
alpha(hsla(100, 50%, 50%, 0.5));

These functions all take arguments which can be color variables, literal colors, or the results of other functions operating on colors. All the above mentioned functions also come in a functionp-variant (e.g. lightenp), which force a given color into HSLuv color space.

Float

Float is a fancy way of saying ‘number’. In CartoCSS, you specify just a number - unlike CSS, there are no units, but everything is specified in pixels.

#line {
  line-width: 2;
}

It’s also possible to do simple math with number values:

#line {
  line-width: 4 / 2; // division
  line-width: 4 + 2; // addition
  line-width: 4 - 2; // subtraction
  line-width: 4 * 2; // multiplication
  line-width: 4 % 2; // modulus
}

URI

URI is a fancy way of saying URL. When an argument is a URI, you use the same kind of url('place.png') notation that you would with HTML. Quotes around the URL aren’t required, but are highly recommended. URIs can be paths to places on your computer, or on the internet.

#markers {
  marker-file: url('marker.png');
}

String

A string is basically just text. In the case of CartoCSS, you’re going to put it in quotes. Strings can be anything, though pay attention to the cases of text-name and shield-name - they actually will refer to features, which you refer to by putting them in brackets, as seen in the example below.

#labels {
  text-name: "[MY_FIELD]";
}

Boolean

Boolean means yes or no, so it accepts the values true or false.

#markers {
  marker-allow-overlap: true;
}

Expressions

Expressions are statements that can include fields, numbers, and other types in a really flexible way. You have run into expressions before, in the realm of ‘fields’, where you’d specify "[FIELD]", but expressions allow you to drop the quotes and also do quick addition, division, multiplication, and concatenation from within CartoCSS syntax.

#buildings {
  building-height: [HEIGHT_FIELD] * 10;
}

Numbers

Numbers are comma-separated lists of one or more number in a specific order. They’re used in line dash arrays, in which the numbers specify intervals of line, break, and line again.

#disputedboundary {
  line-dasharray: 1, 4, 2;
}

Percentages

In CartoCSS, the percentage symbol, % universally means value/100. It’s meant to be used with ratio-related properties, like opacity rules.

Attention

You should not use percentages as widths, heights, or other properties - unlike CSS, percentages are not relative to cascaded classes or page size, they’re, as stated, simply the value divided by one hundred.

In an example:

#world {
  // this syntax
  polygon-opacity: 50%;

  // is equivalent to
  polygon-opacity: 0.5;
}

Functions

Functions are comma-separated lists of one or more functions. For instance, transforms use the functions type to allow for transforms within CartoCSS, which are optionally chainable.

#point {
  point-transform: scale(2, 2);
}

Mapnik Render-Time Variables

Mapnik >= 3.0.0 supports variables of the form @var. These can be used from CartoCSS by specifying them as strings. For example:

#layer {
  line-width: '@zoom';
}

For this to have any effect you have to pass the variables to Mapnik at render time in a hashmap of the form variable_name:variable_value.

Resetting properties

You can reset properties by specifying them with the keyword none. They will then be removed from the symbolizer thus using their default value or not using them at all. This does not work or makes sense for all properties like e.g. not for text-face-name. For an overview over properties where this works or makes sense see this list.