[Talk-GB] OS Boundaries

Chris Hill osm at raggedred.net
Mon Apr 19 18:53:26 BST 2010

John Robert Peterson wrote:
> There is also the quite high level question of what is the "correct"
> position for these boundaries: if a boundary follows a river, and the
> river has changed course by a few meters since this boundary was
> established, does the boundary move with it, or does it stay where it
> was defined?
Boundaries are updated each year, so these boundaries are definitive. 
They are decided by various appointed bodies for each type of boundary 
and then sent to OS for recording. Some boundaries, such as 
parliamentary ones, must be recorded by OS ("The National Mapping 
Agency") as defined in the statue that set up the committee.

If a river moves and these definitive boundaries don't, then the 
boundary doesn't follow the river any more.
> I assume that the errors that you are finding are basedo n the complex
> tweaking of the OS grid that was done to correct for surveying errors
> way back befor they had gps?
I think the OS data is correct, I have checked against paper and digi 
maps. I believe it is a transform problem.
> Do we have a precise definition of these tweaks they made to the grid system?
> What are the magnatudes of these errors?
They vary across my samples, but up to 150m latitude and 40m longitude.

Cheers, Chris

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