Monday 21 June 2021

"With a little help from my friends"

[ Update:  Part II re-uses this and improves the manual for a London area action ]

Part of our mandate at is to raise awareness around climate change issues in East Anglia. A key part is to quantify risks around flooding from land during increasingly variable weather, as well as to predict what sea level rise would look like over time from melting polar ice caps. That combines respectively excellent ground work by DEFRA - see their Future Fens twitter feed - and modelling against topography by Ordnance Survey and DEFRA. And timing of sea level rises is an emotional issue: to balance the reality of the risk with questions around time scales (see comment), will help raise awareness without unduly raising alarm.

click to enlarge (note @ArcGISStoryMaps tee-shirt)

On a recent Human Wave march - a festive event by Extinction Rebellion to appeal to the public in a kinder gentler way than protests - the playful yet serious pirate map of the East Anglia Fenlands-turned-into-archipelago drew the attention of another group in Shropshire and Herefordshire. These are however inland at elevation and thus not prone to sea level rise. Flooding has moreover been in the news the past winters, and a key task is to delineate flood risk areas in valleys and lower elevations areas. Here is a workflow to create such a map, and then to create an interactive 3D model as shown here for East Anglia. 

Note on software: these work in Esri and QGIS, although the 3D part follows the former and can easily be interpolated in the latter. There are also these how-to manuals: Open Data Workshop (28 pp. polar maritime maps incl. QGIS), Sea Level Rise from Open Data (15 pp. incl. flooding in East Anglia), Sea Level Rise in 3D (15 pp. incl. buildings in Cambridge) and maps4campaigns (17 pp., all in Esri and Creative Commons CC BY-SA 4.0).


The ONS Open Geography Portal provides administrative boundaries, of which the medium resolution Counties will suffice here. Posting just the two counties delineates the area, and will allow to cookie-cutter extract the 10m Digital Elevation Model from DEFRA, again sufficient for this purpose. Note the incomplete coverage that will not be an issue for 3D: DEFRA concentrated around low lying areas and the yellow regions are key for flood risk assessment here.

click to enlarge

Risk of Flooding from River and from Sea is a web service ensuring we get DEFRA updates, and it's a comprehensive dataset so zooming in is necessary for it to show as at right above. Or go ahead and pan or zoom around the map here (you may need to zoom in to see Risk of Flooding):

View larger map


This varied terrain will warrant a perspective view, so let's recast what was done in East Anglia, minus the sea level n/a here and the flood defences (tho they may be added, see challenges in previous link). 

Note on elevation surface from open data: Ordnance Survey has 50 m. resolution digital elevation for free and 5 m. for subscription (1 yr. free trial), and DEFRA has 10 m. all under Open Government License. And while these can be used as web services on the desktop, an elevation surface must be created locally to share as custom base on the web. 

First create a 3D scene from the 2D map. As above, make the 10 m. elevation  clipped to the two counties into an elevation surface. Voila! you have an interactive 3D map that helps delineate the flood risk areas w.r.t. topography (you may need to zoom in to see Risk of Flooding, and click on the double right arrow to hide Missing Legend):


Why not give it context, however, in terms of access, facilities etc.? Well EsriUK and OS OpenData provide plenty of that!  Feel free to fly around (you may need to zoom in to see Risk of Flooding and OS Open Roads, and click on the double right arrow to hide Missing Legend):

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