Cite

Helvetia ... Per Gerardum Mercatorem ...

MLA

Helvetia ... Per Gerardum Mercatorem ... 0AD. https://collections.library.yale.edu/catalog/15483163.

APA, 6th edition

Helvetia ... Per Gerardum Mercatorem ... (0 C.E.). [Maps]. https://collections.library.yale.edu/catalog/15483163.