Layers in Mapnik can have multiple borders and multiple copies of other attributes. This ability is useful in drawing line outlines, like in the case of road borders or 'glow' effects around coasts. CartoCSS makes this accessible by allowing attachments to styles:

``css
#world {
line-color: #fff;
line-width: 3;
}

#world::outline {
line-color: #000;
line-width: 6;
}
`

Attachments are optional.

While attachments allow creating implicit "layers" with the same data, using instances allows you to create multiple symbolizers in the same style/layer:

`css
#roads {
casing/line-width: 6;
casing/line-color: #333;
line-width: 4;
line-color: #666;
}
`

This makes Mapnik first draw the line of color #333 with a width of 6, and then immediately afterwards, it draws the same line again with width 4 and color #666. Contrast that to attachments: Mapnik would first draw all casings before proceeding to the actual lines.

Variables & Expressions

CartoCSS inherits from its basis in less.js some new features in CSS. One can define variables in stylesheets, and use expressions to modify them.

`css
@mybackground: #2B4D2D;

Map {
background-color: @mybackground
}

#world {
polygon-fill: @mybackground + #222;
line-color: darken(@mybackground, 10%);
}
`

Nested Styles

CartoCSS also inherits nesting of rules from less.js.

`css
/ Applies to all layers with .land class /
.land {
line-color: #ccc;
line-width: 0.5;
polygon-fill: #eee;
/ Applies to #lakes.land /
#lakes {
polygon-fill: #000;
}
}
`

This can be a convenient way to group style changes by zoom level:

`css
[zoom > 1] {
/ Applies to all layers at zoom > 1 /
polygon-gamma: 0.3;
#world {
polygon-fill: #323;
}
#lakes {
polygon-fill: #144;
}
}
`

FontSets

By defining multiple fonts in a text-face-name definition, you create FontSets in CartoCSS. These are useful for supporting multiple character sets and fallback fonts for distributed styles.

#world {
  text-name: "[NAME]";
  text-size: 11;
  text-face-name: "Georgia Regular", "Arial Italic";
}

<FontSet name="fontset-0">
  <Font face-name="Georgia Regular"/>
  <Font face-name="Arial Italic"/>
</FontSet>
<Style name="world-text">
  <Rule>
    <TextSymbolizer fontset-name="fontset-0"
      size="11"
      name="[NAME]"/>
  </Rule>
</Style>

Filters

CartoCSS supports a variety of filter styles:

Numeric comparisons:

`
#world[population > 100]
#world[population < 100]
#world[population >= 100]
#world[population <= 100]
`

General comparisons:

`
#world[population = 100]
#world[population != 100]
`


String comparisons:

`
/ a regular expression over name /
#world[name =~ "A.*"]
`

#### Installation

If you're using Mapbox Studio Classic, you're already
using CartoCSS and don't need to do a thing.

If you're a developer-type and want to use the carto binary with
node.js (and you have npm installed),

npm install -g carto

Optionally you may also want to install millstone which is required for resolving data in the same way as Mapbox Studio Classic does:

npm install -g millstone


Having millstone installed specifically enable support for localizing external resources (URLs and local files) referenced in your mml file, and detecting projections (using node-srs)

Now that Carto is installed you should have a carto command line tool available that can be run on a Mapbox Studio Classic project:

carto project.mml > mapnik.xml

Available parameters:
* -h / --help - Display help message
* -v / --version - Display version information
* -b / --benchmark - Outputs total compile time
* -l / --localize - Use millstone to localize resources when loading an MML (default: off)
* -n / --nosymlink - Use absolute paths instead of symlinking files
* -a / --api VERSION - Specify Mapnik API version (e.g. --api 3.0.10) (default: 2.3.0)
* -ppi RESOLUTION - Pixels per inch used to convert m, mm, cm, in, pt, pc to pixels (default: 90.714)

#### From code

Currently CartoCSS is designed to be invoked from node.js.
The Renderer interface is the main API for developers, and it takes an MML file as a string as input.

// defined variables:
// - input (the name or identifier of the file being parsed)
var carto = require('carto');

try {
var data = fs.readFileSync(input, 'utf-8');
var mml = new carto.MML();
mml.load(path.dirname(input), data, function (err, data) {
if (err) throw err;
var output = new carto.Renderer({
filename: input,
local_data_dir: path.dirname(input),
}).render(data);
console.log(output);
});
} catch(err) {
if (Array.isArray(err)) {
err.forEach(function(e) {
carto.writeError(e, options);
});
} else { throw err; }
}

$3

To install, download or clone this repository, then copy the vim-carto
directory located at build/vim-carto to your ~/.vim` directory.

cp build/vim-carto/* ~/.vim -R

Credits

CartoCSS is based on less.js, a CSS compiler written by Alexis Sellier.

See also a list of dependencies.

Authors

* Tom MacWright (tmcw)
* Konstantin Käfer (kkaefer)
* AJ Ashton (ajashton)
* Dane Springmeyer (springmeyer)