They are a good way to cut air travel and carbon emissions, particularly where, as in China, they connect dense but distant population clusters.

高铁是减少航空旅行和碳排放的好途径，尤其在象中国这样的地方，它们连接了人口密集但偏远的地区。

As for the question of running out of space, the issue isn't so much about total land in the world as it is that large populations cluster together within cities.

至于空间匮乏的问题，主要不在于全球总土地面积而在于城市中密集的人口聚集。