I have a couple of maps on which I need to project a list of addresses. The problem is that the two maps are in "The Ordnance Survey National Grid reference system" i.e. "British National Grid".
If I project the long/lat of the addresses, obviously, they are not projected in the right spot. I tried a lot of things but I was not able to solve the problem.
I'm open either on transforming the long/lat in something else or transforming the maps.
EDIT: Let's say that I have one map and this map is a shapefile. I wrote that they are not correct because if I have a portion of map of one city (for example London) and I project the long/lat of an address located in London, in ArcGIS the point will be displayed far from the map. In order to project it I used the standard procedure of "display x-y data".
EDIT2: Sorry for the problems, but I'm not really an expert of Gis. I don't know if it is possible to put the URL of the map here, but basically I'm using the Land Registry's INSPIRE Index Polygons
EDIT3: the original file is in the GML format. I first tranform it in a shapefile then, when I import it in ArcGis, the program automatically recognize it with the Projected Coordinate System: OSGB_1936_British_National_Grid