The article is interesting and well-structured, but contains quite a few claims (whole paragraphs included) that are currently uncited. I expect that many of these simply require existing refs to be repeated. I have marked up some examples.
Several images are very large, and almost none are of the default size. We use images at default scale wherever possible (with the parameters |thumb|upright|... for portrait images), and only stray larger in the lead and exceptional cases. I can see there is a desire to portray the maps extra-large, but this too seems overdone, and in the case of other images there seems little justification to avoid the defaults. A double-page spread may possibly need to have double width, but I'd try it first at the default, and only go wider and write a justification (use a comment <!--put reason here-->) if absolutely necessary.
Much the same goes for the use of multiple images, which make maintenance difficult. Best to use single images; if several are really needed, best to use a gallery. When a pair of images definitely belong together (like Palestine and the detail) then it seems reasonable; in other cases, less so.
Lead: please wikilink disciplines, sciences and technical terms, e.g. astrolabe, globe, astronomy, etc etc. Do the same for first usages of such terms throughout the article.
Please link Monachus in the caption of the image in the Antwerp section.
Please label the Palestine map in the Louvain section with its date; I think all the maps including this one should state who made them, as not all are Mercator's. Further, when a map is from an atlas or other book, that should be named also.
Please ensure that all paragraphs are cited - I have marked up some that are not.
"witty epigram" - according to who? If it's an editor's opinion, we should drop the adjective. Same for the various "dangerous", "deadly", "fulsome" - these should be cited directly, if need be by repeating a reference right beside the adjective, even if the sentence or paragraph is already cited. Otherwise they look like personal opinion.
"Many cities have a statue of Mercator" is cited to a list of images, not really evidence. It would be better to say "Cities including Duisburg, Louvain, ... have a statue ..." and to cite each claim to a reliable source. The same goes for the other refs in that paragraph. At the moment they come across as an editor's personal knowledge.
This is a well-crafted, detailed, and now properly-cited article on a major but poorly-known historical figure. The article is a significant contribution to Wikipedia, enhancing it as a global encyclopedia, and is a worthy addition to the list of Good Articles. Congratulations! Chiswick Chap (talk) 12:48, 18 September 2016 (UTC)[reply]