Despite the apparent diversity, the 16th century reader of Cosmographia would have considered these subjects together. In practice, they employed the same people and used similar instruments and techniques. To the Renaissance mind these disciplines could be conjoined because each was concerned with the application of mathematics to positional measurement. Charting planetary motions, establishing positions in navigation and surveying, mapping the globe, even telling the time— all of the things which Cosmographia explained— were considered simply as the geometrical description of the 'cosmos'. The frontispiece to William Cunningham's The Cosmographical Glasse (1559) graphically demonstrates the perceived unity of the cosmographical disciplines.	The Cosmographical Glasse click for larger image
In many ways the unity of cosmography is best demonstrated in the mathematical instrument makers' trade, which used the techniques of, employed the practitioners of and provided the instruments for each of the branches of cosmography. The fact that individual instrument makers could produce instruments for the wide range of cosmographical disciplines indicates that the techniques and instruments involved in each branch, and in instrument making itself, were very much alike. That instrument makers like Gemma were able to play central roles in other areas of cosmography— such as geography and cartography— provides an even more convincing example of the unity of these disciplines. Indeed, Gemma's success as co-author of Cosmographia attests to the centrality of instrument makers in cosmography.	'Gemma's Rings' illustrated in Cosmographia
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