[Talk-GB] Accuracy of cadastral parcel alignment

[Russ Garrett]

On Wed, 3 Mar 2021 at 14:03, Michal Vinarek <vinascz at gmail.com> wrote:
> looks like an interesting claim with the perfect alignment, although I am myself a bit skeptical.
> For example, importing raw cadastral shapefile for Glasgow (from https://ros.locationcentre.co.uk/inspire/) and comparing it to the cadastral overlay shows some misalignment. Not sure if it's just my JOSM mucking up the import/overlay though.

This is likely due to the coordinate system transformation which is
being used to convert between the OS grid and WGS84 (as used by OSM).
I assume that the OSMUK layer uses the most correct transform, but it
is very easy to end up using a simpler and less accurate transform
instead, which is probably what's happened here.

I would expect that, correctly transformed, the Land Registry data is
likely to be more accurate than any aerial imagery source.

Cheers,

--
Russ Garrett
russ at garrett.co.uk