Hi there,

Many thanks to everyone who’s responded, it’s really helpful. It sounds like we can provide the ability to add coordinates, and assume WGS 84, but it would be good to also allow cataloguers to use OS national grid coordinates and enable conversion, so that we can just store lat/long in the EAD. 

cheers,
Jane




On 4 Dec 2014, at 18:31, humphrey <[log in to unmask]> wrote:

> Yes, I am lurking.
> 
> Yes, I think you can safely assume that anyone supplying latitude and longitude as a pair of decimal numbers is using WGS-84.  It is pretty much a standard now, used well beyond GPS, and anyone with actual latitude and longitude in a different format will probably have the sub-degree information as minutes and seconds, which would need a whole other form to input.
> 
> However, I also think that enabling the interface to also accept Ordnance Survey national grid coordinates is important. These are not latitude and longitude at all, but numbers of kilometres east and north from a point south west of Lands End (“grid origin”), and only have meaning within Britain.
> 
> Note that any spatially-enabled database system (we use Postgres) includes functions to convert between coordinate systems, and these usually use the numeric IDs for coordinate systems defined by the EPSG Geodetic Parameter Registry (www.epsg-registry.org). In this, the British National Grid, or "OSGB 1936 “  has SRID 27700, the “European Terrestrial Reference System 1989” is 3034, and WGS-84 is 4326. A UI where there were boxes to type in a pair of coordinates, and a drop-down menu to select the coordinate system, would work so long as you had that conversion functionality. I would store everything as WGS-84.
> 
> If anyone has found the maps in our Vision of Britain site a little odd-looking, it is because it is built around ETRS-89.
> 
> … and I will now ask my own obscure question ….
> 
> Humphrey
> 
>> On 4 Dec 2014, at 17:38, Jane Stevenson <[log in to unmask]> wrote:
>> 
>> Hi there,
>> 
>> A rather specialised question, but geographers may lurk on this list….(Humphrey…are you there?)
>> 
>> I’m looking at enabling Archives Hub contributors to add geographical coordinates to the geographical names they enter.  But apparently latitude and longitude are not as straightforward as I thought.
>> 
>> There are a number of systems that can be used, and the system you use can affect the entry. 
>> 
>> Wikipedia: "Latitude and longitude values can be based on different geodetic systems or datums, the most common being WGS 84, a global datum used by all GPS equipment.  Other datums are significant because they were chosen by a national cartographical organisation as the best method for representing their region, and these are the datums used on printed maps. The latitude and longitude on a map may not be the same as on a GPS receiver. Coordinates from the mapping system can sometimes be roughly changed into another datum using a simple translation. For example, to convert from ETRF89 (GPS) to the Irish Grid add 49 metres to the east, and subtract 23.4 metres from the north.”
>> 
>> We can hardly expect archivists to know whether they are using WGS84 or OSGB36 (which the OS use) or something else. But this seems to mean that if you put Lat: 54.428736 Long: -2.961333 it could in theory refer to a slightly different point depending on the system you are using. There is not a universally agreed and implemented system.  Would it be terribly bad for us to assume WGS84? Should we just avoid adding anything about the system used?  WGS84 is what is used by GIS systems apparently, so I assume online lookups such as http://www.latlong.net/ use it, but archivists may well refer to OS maps for their lat/long. 
>> 
>> cheers,
>> Jane
>> 
>> Jane Stevenson
>> The Archives Hub
>> T   0161 275 6055
>> W  archiveshub.ac.uk
>> Skype janestevenson
>> Twitter @archiveshub, @janestevenson
>> J Floor, Sackville Street Building,  Sackville Street, Manchester, M1 3BB
>> 
>> jisc.ac.uk
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> 
> Humphrey Southall
> Professor of Historical Geography/
> Director, GB Historical GIS
> University of Portsmouth
> Geography Dept, Buckingham Bldg,
> Lion Terrace, Portsmouth PO1 3HE, UK
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