It seems obvious that Cosmographia would have been a likely purchase for a 16th century mathematician, cartographer or instrument maker; the reasons for its popular success are not so obvious. Nevertheless, one reason for Cosmographia's popularity can be readily located in renaissance perceptions of mathematics and cosmography. During the Renaissance, cosmography was not counted among the disciplines of the academic university curriculum. Rather, like other mathematical sciences it was considered a practical and utilitarian art. Such things as the record of large instrument orders from sea trading companies for use in navigation and the establishment of astronomical observatories by members of the ruling classes demonstrate that important commercial and political entities saw cosmography as useful. As it turns out, their faith in cosmography as a means of solving practical problems was not at all misplaced. When a solution to the problem of determining longitude at sea was finally achieved in the 18th century, it was based upon techniques first suggested by Apianus and Gemma. One method (the measuring of lunar distances) was introduced by Apianus in Cosmographia. Another (using portable clocks to determine differences in local time) was suggested by Gemma in a later publication.	"Triangulation"-a useful and important surveying technique-first appeared in Gemma's enlargement of Cosmographia
	Apianus' illustration of measuring lunar distances in Cosmographia
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