# CartoCSS指南

### 4.5 理解元瓦片

#### 元瓦片的结构

There are two main parts to a metatile: the tiles and the buffer. By default a metatile in TileMill consists of 4 tiles (arranged 2 wide and 2 high) and a buffer of 256 pixels around the tiles.

#### 调整元瓦片配置

Map {
background-color: white;
buffer-size: 256;
}


#### 合理设置元瓦片尺寸

##### 增大元瓦片尺寸
###### 原因1：减少导出时间

While disabling metatiling can give a more responsive feel to the map UI, the opposite is true when exporting to MBTiles. Increasing the metatile size can significantly increase overall performance and decrease the overall time it takes to render an entire export job. This is because rendering many tiles in sequence using larger metatiles means doing less overall work.

#### 参考文献

1. Mapbox, Understanding Metatiles