Epitomizing the scientific currents animating the Royal Society, this map by Edmond Halley reflects a growing understanding of dynamic equilibrium and the sense that different natural forces interact within a single, comprehensible system. Its most significant features are the engraved bands showing the prevailing winds, and the isogonic lines introduced by Halley to show variances in the Earth’s magnetic field. The limited scope of the map—covering only the area between 35 degrees North and South—is a function of limits in the magnetic compass, a device that becomes increasingly unreliable as it approaches either pole. Where the less scientifically rigorous cartographers from earlier ages may have added anthropomorphic touches like wind heads, Halley adds nothing. Instead, he adjusts the layout of the map, limiting its range to what can be definitively measured, leaving no room for anything needlessly whimsical or speculative.
With the addition of new categories of cartographic information, this chart signaled a profound shift in what maps were presumed to show, and for what purpose. Where earlier maps dealt solely with geographic arrangements, charts including visualizations of quantifiable forces offered a valuable frame of reference to those in the emerging scientific community, where meticulously objective information could simultaneously spur and check the development of mechanical theory. As such, it represents a layer data visualization applied above the base used to draw geographic forms. While maps had always played a role in projecting human power in the world, this map was among the first to chart the way natural power operates independently, both facilitating and circumscribing the range of human endeavor.