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I have to work between OSGB1936 and WGS84 and BOTH of these data sets started out life as OSBG1936 BounaryLine data.

I thought I was just at the end of a full revision of my master mapping until I was presented with this OTF Enabled! I use QGIS on both PC and Mac platforms and some of these files date back to work I did three years ago when I was much less proficient than the enthusiastic amateur I am now.

And whilst I have been through many many levels of processing and manipulation I rarely reproject.

For some reason back in the past I also seem to have invoked WGS 84 / UTM zone 30N ESPG:32630 (suspect that was me trying to do a best fit betwixt the two)

But I have OnTheFly projection turned on... this shouldn't happen surely? And more importantly, How do I get them BACK to the same space?

I realise that I must have to do a form of re-projecting- but don't even know where to begin with determining what shits I need nor how to calculate them

Command line, GDAL, OGR and Python are all a scary closed book to me unless I have explicit instructions (I still don't know where or how I would enter a command line statement in QGIS!)- I'm a GUI man all the way.

  • Maybe it's quite obvious, but nevertheless: When you open the layer properties of your layers what information do the CRS sections in the general tabs display? – TobsenB Mar 18 '16 at 11:17
  • You can right-click the layer and use the Save As... option to reproject to another CRS. For Great Britain, I tend to use EPSG:7405 (same as the original CRS they came in: OSBG 1936/British National Grid) – Joseph Mar 18 '16 at 11:20
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    27700 is the more commonly used EPSG code for British National Grid. But yeah the first step would be to see what they say in the "General" tab. Also if you turn off on the fly, what do the co-ordinates look like for where the datasets are. – HeikkiVesanto Mar 18 '16 at 11:26
  • GIS SE is a question/answer database. Please strip out the discussion-board qualities of this post to format a better question. As Sgt. Friday would say, "Just the facts, sir, just the facts." Unfortunately, sometimes when you mangle your data, you just have to roll back to your last backup. – Vince Mar 18 '16 at 11:37
  • Vince- sorry but I disagree- the question is explicit- how do I get them back to the same space – Richard Colwill Mar 18 '16 at 11:38
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You can take a third datasource as reference.

Set the project CRS to EPSG:3875, and load an Openstreetmap background with the Openlayers or QuickMapService plugin.

Then you can easily see which of your datasets is in the right place, and which has a wrong CRS assigned. You can change the second with Set Layer CRS.

If the misplaced layer is a small spot off the Nigerian coast, it is surely in degrees, but wrongly assigned a projected CRS. If the misplaced shape is about 5500km south (overlapping Ivory Coast), a bit smaller as the right one, it is a National Grid shape wrongly assigned as UTM 30N.

Note that EPSG:4277 OSGB36 and EPSG:27700 OSGB36 British National Grid are different. The first one is in degrees, the second is in meters.

  • Andre Thank you for the excellent advice on spotting the UK over Africa- it's really helpful in explaining to my Ultra-noobs how to spot what's wrong and the similar but differing symptoms – Richard Colwill Mar 21 '16 at 12:13
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Thank you all for the assistance- the answer was about as dullard as one could get and a transposition of numbers whilst assigning a Projection

ESPG:32630 (WGS 84 / UTM zone 30N ) had managed to become ESPG:32360 (WGS 72 / UTM zone 60S ) at some point in the past and I was wilfully misreading the latter to be the former.

The moral of the story is to check both the ESPG AND the name of the CRS, in case your own tired eyes are deceiving you

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