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
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