ordnance-surveyqgisunited-kingdom
I'm totally new to GIS. However, I've proudly managed to create a map, which is correctly geo-referenced with a Great Britain Ordnance Survey (OS) background (streetview level) and I've added some point data.
How do I create or import a layer with the OS grid lines?
Coordinates in kml files are usually in lat/long degrees. You can open the file with a text editor to check sample data points. So the coordinate system should be EPSG:4326 WGS84 (not WGS84 Web Mercator) .
Your Ordnance Survey data will probably have metres as units.
Degrees get smaller towards the poles. That's why you can not easily warp the kml to a projected map with photoshop.
You need a reprojection from WGS 84 to British OS. I would use Quantum GIS for that. You can also add a Google background with the openlayers plugin.
For the meridian, the answer is simple: It lies almost in the middle of England, this meridian will be parallel to the local transverse mercator grid, while the others have minimal bendings. This is how the OSGB grid looks on a lat/lon map:
For the parallel, it does not make a difference for the projection which one you take for as center. German tmerc Gauss-Krueger projections use the aequator.
Maybe they intended to use Jersey as origin, but then decided to cut of the first 100km.
The 100km grid is actually a subsystem of a 500km grid which is indicated by the first grid letter, as explained here: Eastings/Northings OSGB36 Grid origin
Best Answer
You can find the OS Grids here
https://github.com/charlesroper/OSGB_Grids
Download the shapefiles and then load them in
You will probably need to adjust the styling and turn on labelling using the tile name as a text label