carto/files/demo.layers

[{
    "id": "world",
    "name": "world",
    "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs",
    "Datasource": {
        "file": "http://tilemill-data.s3.amazonaws.com/world_borders.zip",
        "type": "shape",
        "estimate_extent": "true",
        "id": "world"
    }
},
{
    "id": "countries",
    "name": "countries",
    "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs",
    "class": "countries two",
    "Datasource": {
        "file": "http://tilemill-data.s3.amazonaws.com/world_borders.zip",
        "type": "shape",
        "estimate_extent": "id",
        "id": "countries"
    }
}]