Friday, 13 May 2011

More temporal web maps

Here is last year's Fenlands mashup on 2nd gen. beta (this data is also posted on the UK academic ShareGeo site and the apps site):

Following on my previous post comparing satellite imagery over time on ESRI's Change Matters, you can also compare here the change in landcover from 1877 to today. This map is public, simply turn off all layers but EastAngliaCounties (reference), CambsSurfGeoMap (1877) and GBR BGS (current surficial lithology). The metadata will tell you the scanned image is from Darby's book relating the surficial geology from Skertchley's Geology of the Fens in 1877. Current surficial geology is from British Geological Survey's web mapping service onshore map.

Screenshots of current (L) and 1877 (R) geology with semi-transparent overlay (C)

Select CambsSurfGeolMap, then move the slide-bar button at bottom left, and see the change in land cover over almost a century and a half. You can see the good correlation in the Fenland silt (tan and fine stiple), the peatlands (brown and coarse stipple), gravel beds (light purple and hachure) and clay (white and transparent). Note however near the center of the map that peatlands extend a lot further south in 1877 (coarse stipple) than today (brown), indicating not an insignificant retreat. Likewise to the southwest the clay retreated significantly from 19877 (black) to today (dark purple).
Darby documents the changing geomorphology during the drainage of the fens (retreating peatlands) to increase the extent of arable land (retreating clay top). This mash-up makes the change from 1877 to today patently visible through a simple slide-bar... probably one of the best uses of maps!