Mercator (mystery word)

Mercator: In the sixteenth century Gerardus Mercator popularized the Mercator projection for global maps. This is a cylindrical projection (the spherical earth is projected onto a cylinder). While this projection is locally accurate, especially maintaining compass headings, as the maps get farther from the equator, east-west distances are distorted - with infinite distortion at the poles. That said, I can not imagine the author's intent in the use of this word.

Claude watched the mercator of sunlight advance up the field.