Tracking the competition with spy satellites

In October, the Chinese province of Guangdong — the manufacturing center on the southern coast that drives 12 percent of the country’s economy — stopped publishing a monthly report on the health of its local factories.

For five consecutive months, this key economic index had shown a drop in factory production as the United States applied billions of dollars in tariffs on Chinese exports. Then, amid an increasingly bitter trade war between the United States and China, government authorities in Beijing shut the index down.

A small startup in San Francisco began rebuilding the index, lifting information from photos and infrared images of Guangdong’s factories captured by satellites orbiting overhead.