Naïvely, because of his Latin name, I had assumed Mercator was Italian, probably based in Venice. In fact, Gerard Kremer was born in what is now Belgium, and assumed the name Mercator on the death of his parents.
In the early sixteenth century, life in the Low Countries was turbulent, with frequent famine and religious persecutions. As a cobbler's son, Mercator had no privileged position, but through an uncle in the Church, he secured a place at Louvain University. Dabbling in philosophy, he found himself uneasy with religious doctrines, and eventually turned to 'cosmography', applying his knowledge and learning the trade of globe and instrument-making. Mercator became well known particularly for his engraving skill. In later life his printed maps became more abstract and mathematical, and more difficult for people to understand. As well as a maker of maps, globes, and instruments, Mercator also wrote various religious commentaries and philosophies, neither entirely happy with established doctrine, nor seeking conflict with the authorities.
The picture of the man that emerges from Crane's book is one of Job-like patience, combined with hopeless optimism, always massively underestimating the duration of his various projects. His Atlas remained incomplete at his death, aged over 80, and was completed by his surviving sons. The book's style is rather dry, but this probably befits its subject.
As a "popular" science book, it is disappointing but perhaps not surprising that there is only the scantest explanation of Mercator's Projection, but this is the device through which his name has passed into history. Derived at a time without the benefit of calculus or (probably) even logarithms, Mercator's mathematical achievement was substantial, but is apparently beyond explanation to today's more educated public (though the maths on the Wikipedia link isn't for the faint-hearted; I assume Mercator took a more geometric, holistic approach, that ought to be more accessible). The projection has the benefit that straight lines represent lines of a constant compass bearing, so it is extremely useful for navigation, even though these lines do not generally represent shortest distances. Although Crane mentions this, I think he doesn't really give it enough emphasis, so it's easy to misunderstand the importance of the benefits of the projection. Mercator's Projection is not the best general way to achieve a whole-world view any more, because of the enhanced distortion of higher latitudes, but too often it is unfairly accredited with a tag of Imperialism because of its depiction of Europe and North America relative to Africa and the tropical latitudes. Perhaps in an unconscious attempt to redress this imbalance, Crane gives equal proportion to all of Mercator's work, which is of benefit in many ways, but in others, occludes his greatest creation.