UKC

Anyone know why OS mapping of NI is tilted in the OS app? Screengrab to illustrate: with one from Scotland showing it level.

Maybe that OSNI 1952 grid vs. OSGB grid are different and the simplest approach was to distort the NI maps. 

Yes; they're reprojecting the OSNI grid mapping into the OSGB grid. So it is rotated.

I'd also check to see which grid the OS app is actually using; it may be WGS84 rather than OSGB. Check for rotations in the W & E extremes of GB,

Yes - I think it will be that. Grids only work well over a limited east-west so the island or Ireland has a different one. A NI map will match up with Republic of Ireland map.

The app is grid north up for OSGB grid. 

There's a border in the middle of the Irish Sea. 

There's something going on there I think. If you look at Lewis and zoom out so that no OS maps are shown and then zoom up until they are the grid is rotated slightly. But if then the deliberately rotate and then set it back to North up the grid is no longer rotated. 

From the app development point of view maybe it uses a standard tile viewer (webmercator) with some tweaks at certain zoom levels. 

That's interesting - I was there last summer on holiday, and I'm pretty certain NI wasn't covered by OS? I think I tried using the OS app on my phone and it didn't work. Am I just misremembering?

Yes. The whole of Ireland (Republic and North) share the same reference grid and because Ireland is several hundred kms to the west of the prime meridian the surveyors agreed to apply one grid across the whole island. The fact that OSGB is north at the top rotates the UK in terms of the grid. Just look at the lats and longs around the maps to see how much rotation there is.

No, you're quite right.  I almost bought the NI mapping on Viewranger (along with the 1:50k OSI maps that I did buy) for my trip to Ireland in 2019.  At the time that seemed to be the only way to even get a good look at them short of buying paper copies.

Thanks all 

Still, they could adjust the app display. Viewranger managed this...its impractical to be displaying tilted text etc. on a mapping service for outdoor use.

They seem to share a bit more than that as well. 

The NI maps look exactly like OSI maps (colour scheme, symbols etc. - a bit different to GB OS ones).  Zoomed out it looks like it strictly covers Northern Ireland only, but when you zoom in a bit the mapping continues across the border to cover a rectangular area that includes most of the rest of Ulster too (including all of County Donegal) and continues to the West just beyond Sligo.

As I mentioned above I bought a full set of (Republic of) Ireland OSI map tiles on Viewranger, and I'm sure the reverse was also true - the mapping extended a bit beyond the border into NI to make a neat rectangular area.  But funnily enough looking at that map now on the Outdooractive app, it seems to have been redacted since then - it's now blacked out much more closely along the line of the border itself.  Perhaps OA are a bit more averse to giving people a little bit extra for free than VR were.

Oops - too late to edit to correct that.  That's only at 250k(?), when you zoom in further to the 50k map it follows the border a bit more closely.

Thanks

That approach makes little sense though for end use. If I'm opening up an OS map for a region in NI, well that's where I'll be using it. Why adjust to OSGB and give me tilted grid lines and text? Sorry to find another deficiency in the OS app compared to Viewranger.

Can you rotate the mapping? OruxMaps allows you to do that with ease. Sometimes too much ease, so you do it accidentally (two finger twist).

But OruxMaps is a fully-featured mapping app. Shame the OS sent the vampires after him for using OS mapping via Bing.