With references to historical materials in Manchu and Chinese languages, this article analyzes how the espionage network established by the Zheng family operated during the Ming-Qing transition, and explores how the Qing Empire used intelligence from this network to acquire knowledge of islands on the southeastern coast and Taiwan before their conquest in 1683. This article argues that the Zheng espionage network conducted secret spying missions in China proper collecting detailed intelligence, which was in turned obtained by the Qing Empire, also through espionage, for learning about Taiwan and the neighboring islands prior to conquering them. The Taiwan Lue Tu (the brief map of Taiwan), archived at the National Palace Museum, was drafted under this background. This sketch map not only served military purposes but also constituted the basic understanding of the Qing Empire on Taiwan. The cartography of Taiwan included the Chinese version made by the Zheng commanders and the Manchu version constructed by the Qing court. Manchu descriptions on the map reveal that the Qing court perceived itself as a universal empire. By understanding how the Zheng espionage network operated and how the Qing Empire exploited its intelligence, this article examines how the Qing court transformed Taiwan into an imperial borderland within the context of imperial history.