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The development and evolution of the William Smith 1815 geological map
                       from a digital perspective

GSA TODAY | JULY 2016  Peter Wigley, Lynx Geographic Information Systems Ltd, 93-99          distance from one Market Town to another with the exact admea-
                       Upper Richmond Road, Putney, London SW15 2TG, UK                      surement prefixed to each from the Metropolis [London]” (Cary,
                                                                                             1796). Cary was aided in this task by material provided by the Post
                       ABSTRACT                                                              Master General, but he also undertook a number of local, detailed
                                                                                             triangulated surveys in order to complete the map. The map was
                         William Smith’s 1815 geological map of England and Wales            produced at a scale of approximately one inch to five miles
                       is a masterpiece; the map differs from all other contemporaneous      (1:316,000) and Cary was to use this map as the basis for the 1815
                       maps in that Smith applied the principles of stratigraphy to its      Smith map.
                       construction. The maps are extremely rare and therefore not
                       readily available for study and analysis; however, over the past        Figure 1 illustrates how the base map was compiled; the three
                       decade a number of Smith geological maps have been digitally          maps are from part of the county of Wiltshire. The top map (A)
                       scanned and some incorporated into a Geographic Information           is from Cary’s 1794 New Map of England and Wales and shows
                       System (GIS). Early nineteenth-century maps of the United             in extraordinary detail roads, canals, rivers, towns, and villages
                       Kingdom (UK) present a number of difficulties when trying to          included by Cary. The middle (B) map is a de-colored Smith
                       build them into a GIS, mostly related to projection problems and      1815 map and shows how Cary and Smith simplified the road
                       the fact that many pre-date the “1st Principal Triangulation” of      network, reduced the number of towns and villages located (and
                       the UK. However, once in the GIS, they can be used with great         reduced the size and style of the typeface), while at the same
                       effect to show the evolution of Smith’s maps and also to compare      time emphasizing topographic features. Incidentally, Cary, ever
                       his maps with modern geology. When combined with digital              mindful of commercial implications, ensured that the outlines
                       terrain data, Smith’s maps can be displayed in 3D.                    of the estates of wealthy landowners were always included. This
                                                                                             map also shows Smith’s engraved geological lines. Map (C) is the
                       NINETEENTH-CENTURY MAP TECHNOLOGY                                     corresponding part of the 1815 map, which was hand-colored to
                                                                                             show the geology.
                         William Smith (1769–1839) was an undoubted geological
                       genius with an amazing eye for the countryside and an ability to        Smith’s geological mapping was not limited to the great 1815
                       think in three dimensions. He was also an expert surveyor,            map. Between 1819 and 1824, John Cary published, in six parts,
                       apprenticed in his youth to Edward Webb (1751–1828) at Stow-on-       Smith’s geological maps of 21 English counties. The New
                       the-Wold, where he learned to measure and value land during the       Geological Atlas of England and Wales was used for its base maps.
                       time of the Enclosure Acts (Torrens, 2001). This skill may have       The large county sheets of Cary’s New English Atlas have been
                       classified him as an artisan in the eyes of the gentlemen of the      described as “remarkable for their accuracy and their clear, clean
                       Geological Society of London and thus precluded his membership        print brilliantly engraved, and rank with the Ordnance Survey as
                       of the Society; however, it was to prove essential in the production  the finest maps of the nineteenth century” (Tooley, 1952). Smith
                       of the great map. Through use of sextant, plane table, and other      could not have had a finer set of topographic maps upon which to
                       surveying instruments (the high-tech of the time), Smith was able     draw his geological lines.
                       to locate outcrops on his field maps. Today with GPS, laser range-
                       finders, and access to remote-sensing data, the whole process of      SMITH’S REPRESENTATION OF GEOLOGY ON THE MAP
                       map making is very much easier than it was in Smith’s day—yet,
                       for all that, some eighteenth- and nineteenth-century maps of           Smith’s initial problem was how best to show the distribution of
                       England are remarkably accurate.                                      his strata on maps. Should it be by point locations, lines, or colors?
                                                                                             As we know, Smith chose a combination of both line and color.
                         It is highly unlikely that Smith’s map would ever have been         His colors generally had some lithological significance and indeed
                       made were it not for the help of John Cary (1755–1835). Cary was      are still used today. Smith also used graded tints on his maps, with
                       a mapmaker, engraver, and publisher; he probably first met Smith      the strongest color at the base of the bed at outcrop, lightening
                       when he engraved his plan of the Somerset Canal in 1793               upward. This is what Smith says in his memoir to the map:
                       (Torrens, 2007, p. 13). At that time, Cary’s maps were some of the
                       best available. In 1794, he was commissioned by the Post Office to         The Society of Arts very wisely foresaw, in offering their
                       map towns and roads on his New Map of England and Wales. At                premium for a mineralogical map (which I have just had
                       that time, postal charges were based on distance, and it was there-        the honour to obtain), that one of the greatest difficul-
                       fore important to the Post Office that Cary show “the actual               ties in understanding such an extensive branch of
                                                                                                  natural history arose from the want of some method of
                                                                                                  generalizing the information, which could only be

     GSA Today, v. 26, no. 7, doi: 10.1130/GSATG279A.1.

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