Thursday, 29 December 2011

On-line spatial data validation, part II

[2013 update: Socium is now 1SpatialCloud]

Three weeks ago I introduced Socium's Online Validation Service (OVS). I showed the Ordnance Survey vector data QC, on the UK Parishes used as a geographic unit for the Medieval Fenlands project. Two weeks ago Socium kindly created a new rule, to post unexpected variations in adjacent feature attributes. In an essentially agricultural era, economic wealth of the Domesday period was quantified by Darby via the number of plough teams per parish. That is the attribute the rule was written for (it's hard-wired right now and Socium plans to add metadata pick lists in the future).

click image to enlarge

Notice how clean and straightforward the presentation screen is. The result is a set of points along the joint vertices where attributes, scaled from 0 to 5, jump by more than 1 unit among adjacent polygons. That helps find errors in the attributes that were manually entered from Darby map plates, and therefore most prone to errors. A later post will explain an attempt to establish that, or any other correlation with surface geology for example.

click image to enlarge

While this example may appear somewhat trivial, as the colours pop out where there are abrupt transitions, here are a few uses that we'll explore later on:
  • for very large numbers of polygons (1911 for East Anglia alone)
  • concatenate the points into barriers and geoprocess that with imagery or lithology
  • run statistics for the purposes of quantifying the QC applied to a project
Stay tuned for more work on OVS. Thanks again to Socium for deriving this rule so quickly.