Think in terms of a subway map, but add in layers of data like water and sewer lines, power grids, and real time traffic information.

例如，在地铁地图上增加其他一些数据，如供水和排水管道、电网和实时交通信息等。

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He will get a map without sewer and water systems, fire hydrants, and manholes.

NPR: Security Officials Seek to Block Some Online Maps