बाहरी दुनिया से ऐतिहासिक रूप से अलग-थलग रहने के कारण किस शहर को 'फॉरबिडन सिटी' (निषिद्ध शहर) कहा जाता है?

In traditional anthropological classification of human races, which racial group was characterized as 'yellow-skinned'?

What is the approximate estimated proportion of ecumene (habitable) and non-ecumene (uninhabitable/sparsely inhabited) areas on the Earth's surface?