Saturday, 24 April 2010

Post-medieval Fenlands GIS

Let's look at the geographic history of land cover and surface geology of East Anglia after the Civil War , based on Ordnance Survey OpenData and British Geological Survey web mapping services (WMS). My previous posting discussed H.C. Darby's historic & geographic economics of East Anglia Fenlands between the Domesday census and the Civil War.

The 1794-1813 agricultural land cover was derived by assigning a land cover class per parish from Darby's The Draining of the Fens (detailed here) - the map-figure's odd projection precludes its proper registration to the GIS map - this is a gross approximation, but it matches Darby's classification by parishes (posted here). The ~1800 land cover and the 1641 Subsidy classes correlate quite well: this supports Darby's conclusion that the economic regime didn't vary much after the Midlle Ages.
(click on image to enlarge)

Let's now use surficial geology maps, which can be referenced directly - or mashed up - to the GIS map. The 1877 surficial geology of Cambridgeshire in Darby's book is registred to parishes, and can thus be georeferenced to the GIS map. And the current surficial geology from BGS' WMS (detailed here) is posted directly as a GIS layer.
(click on image to enlarge)

The ~1800 land cover and the 1877 surficial geology correlate well, given the approximations of the former. The 1877 and current surficial geology also correlate well, but subtle differences can be seen: silt and peat have similar extents, as do clay in the north central and southeastern Cambridgshire; however the clay belt running SW-NE at centre appears to have shrunk significantly from the 1877 to the current survey. The map-figures being registered to parishes and the WMS at 1:625,000 scale, this bears further examination at much larger scales and on the ground.
GIS is a great way to highlight similarities and differences over time. And suggest further investigation - are the data reliable? are the differences real? are the processes undertood? etc. The great variety of data coverage across time, moreover, points to further research for each period- will this exposé encourage you to find your own? And to help along, this will be posted on the web as a mash-up here.
PS: BBC TV's Mapping the Medieval Mind makes this very topical: "Maps delight, they unsettle, they reveal deep truths, not only where we are, but also who we are". Also the British Library's blog on same.