The map reference is Y4.

地图编号为Y4。

《牛津词典》

As online shopping, online map reference for reference only, such as a little bit different without notice.

由于网络购物，网上的图参只供参考，如有点差异恕不另行通知。

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To combine the scheme and classification maps for a deliverable, a higher-level map can refer to both maps using a DITA map reference (see Figure 6).

要把方案图和分类图组合起来形成可以发布的内容，可以用dita图引用，在更高层次的图中引用这两个图(请参阅图6)。

youdao

The signs contain the place name and a map reference which people can give coastguards when reporting an incident.

BBC: South West Coast Path gets 500th 'life-saving' sign

Each missile comes with a terrain contour matching radar, which compares a stored map reference with the actual terrain to fix the missile's position.

BBC: Tomahawk cruise missile