Spectacular 1874 thematic map of British lighthouses

Lithographed by Robt. J. Cook & Hammond, BRITISH LIGHTHOUSE CHART OF GENERAL COAST LIGHTS. Compiled from authentic sources by Woolfield H. F. Hardinge. London: J. D. Potter Admiralty Chart Agent, 1874.
Lithograph printed in four colors, 32 5/8”h x 23 5/8”w plus margins. Lined with linen at an early date.
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A rare and striking 1874 thematic map of lighthouses of the British Isles, and a superb example of the visual display of quantitative information.

The map depicts in outline the British Isles and part of the French coast, with the locations of more than 250 lighthouses, each indicated by a small geometric figure. Two insets provide large-scale views of the complexes of lighthouses between Deal and Yarmouth and at the mouths of the Mersey and Dee Rivers. With extreme visual economy, the geometric figure for each light encodes data for its color, range, frequency and sweep. Taken together, the color scheme and the profusion of geometric figures, all set against a dark gray ground, produce a striking and decorative effect.

A note under the title guides the viewer “for descriptive particulars of the Lights see list published with the Chart.” This is presumably the Key to British Lighthouse Chart, also published by J.D. Potter, which COPAC describes as a “table listing names and details of lighthouses.”

The Lighthouse Chart and Key seem to have been Mr. Hardinge’s only publications, and his very identity is a mystery. An internet search yields only two mentions of the name: a Warden of Christchurch, Eltham from 1884-1890; and the husband of one Isabella Hardinge (born ca. 1846), with whom he had two children.

References
As of February 2018, COPAC lists examples only at the British Library, National Library of Scotland, and Oxford University. OCLC gives no locations in America.

Condition

Some surface soiling and a bit of wrinkling, about very good.