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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
Upper Richmond Road, Putney, London SW15 2TG, UK
ABSTRACT
William Smith’s 1815 geological map of England and Wales
is a masterpiece; the map differs from all other contemporaneous
maps in that Smith applied the principles of stratigraphy to its
construction. The maps are extremely rare and therefore not
readily available for study and analysis; however, over the past
decade a number of Smith geological maps have been digitally
scanned and some incorporated into a Geographic Information
System (GIS). Early nineteenth-century maps of the United
Kingdom (UK) present a number of difficulties when trying to
build them into a GIS, mostly related to projection problems and
the fact that many pre-date the “1st Principal Triangulation” of
the UK. However, once in the GIS, they can be used with great
effect to show the evolution of Smith’s maps and also to compare
his maps with modern geology. When combined with digital
terrain data, Smith’s maps can be displayed in 3D.
NINETEENTH-CENTURY MAP TECHNOLOGY
William Smith (1769–1839) was an undoubted geological
genius with an amazing eye for the countryside and an ability to
think in three dimensions. He was also an expert surveyor,
apprenticed in his youth to Edward Webb (1751–1828) at Stow-on-
the-Wold, where he learned to measure and value land during the
time of the Enclosure Acts (Torrens, 2001). This skill may have
classified him as an artisan in the eyes of the gentlemen of the
Geological Society of London and thus precluded his membership
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
surveying instruments (the high-tech of the time), Smith was able
to locate outcrops on his field maps. Today with GPS, laser range-
finders, and access to remote-sensing data, the whole process of
map making is very much easier than it was in Smith’s day—yet,
for all that, some eighteenth- and nineteenth-century maps of
England are remarkably accurate.
It is highly unlikely that Smith’s map would ever have been
made were it not for the help of John Cary (1755–1835). Cary was
a mapmaker, engraver, and publisher; he probably first met Smith
when he engraved his plan of the Somerset Canal in 1793
(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
map towns and roads on his New Map of England and Wales. At
that time, postal charges were based on distance, and it was there-
fore important to the Post Office that Cary show “the actual
GSA Today, v. 26, no. 7, doi: 10.1130/GSATG279A.1.
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distance from one Market Town to another with the exact admea-
surement prefixed to each from the Metropolis [London]” (Cary,
1796). Cary was aided in this task by material provided by the Post
Master General, but he also undertook a number of local, detailed
triangulated surveys in order to complete the map. The map was
produced at a scale of approximately one inch to five miles
(1:316,000) and Cary was to use this map as the basis for the 1815
Smith map.
Figure 1 illustrates how the base map was compiled; the three
maps are from part of the county of Wiltshire. The top map (A)
is from Cary’s 1794 New Map of England and Wales and shows
in extraordinary detail roads, canals, rivers, towns, and villages
included by Cary. The middle (B) map is a de-colored Smith
1815 map and shows how Cary and Smith simplified the road
network, reduced the number of towns and villages located (and
reduced the size and style of the typeface), while at the same
time emphasizing topographic features. Incidentally, Cary, ever
mindful of commercial implications, ensured that the outlines
of the estates of wealthy landowners were always included. This
map also shows Smith’s engraved geological lines. Map (C) is the
corresponding part of the 1815 map, which was hand-colored to
show the geology.
Smith’s geological mapping was not limited to the great 1815
map. Between 1819 and 1824, John Cary published, in six parts,
Smith’s geological maps of 21 English counties. The New
Geological Atlas of England and Wales was used for its base maps.
The large county sheets of Cary’s New English Atlas have been
described as “remarkable for their accuracy and their clear, clean
print brilliantly engraved, and rank with the Ordnance Survey as
could not have had a finer set of topographic maps upon which to
draw his geological lines.
SMITH’S REPRESENTATION OF GEOLOGY ON THE MAP
Smith’s initial problem was how best to show the distribution of
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.
His colors generally had some lithological significance and indeed
are still used today. Smith also used graded tints on his maps, with
the strongest color at the base of the bed at outcrop, lightening
upward. This is what Smith says in his memoir to the map:
The Society of Arts very wisely foresaw, in offering their
premium for a mineralogical map (which I have just had
the honour to obtain), that one of the greatest difficul-
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