Projection, Scale, and Accuracy in the 1721 Kangxi Maps

Abstract

The Kangxi Emperor employed Jesuit brothers (1708–18) to produce maps of the provinces of China using a combination of Western and Chinese survey methods. The maps were completed by 1721. They were sent back to Europe and became the basis for maps of China produced by Jean Baptiste Bourguignon d'Anville in 1735. The main changes from traditional Chinese mapping were to use latitude and longitude as primary coordinates, map them using a spherical projection, and use astronomical measurements of latitude and longitude to establish baselines. Changes in latitude and longitude were found using traditional metric survey and relationships between distance north–south and latitude and distance east–west and longitude to convert to degrees. A digitized facsimile of the 1721 map series is available from the US Library of Congress. In this article, the digitized images were used to reconstruct the parameters of the sinusoidal projection, establish scale, and re-project and mosaic the maps into various forms for presentation. The accuracy of five of the province maps is discussed in detail. It is found that poor astronomical measurements of longitude are the most serious issue for the maps, but that apart from areas distorted by the poor longitude estimates, the accuracy was commensurate with that of European land maps of the time.