# Is there a way to determine the datum used when all you have is a lon and lat?

I have a dataset of US intersections from 2011 that I'm going to be using in a project together with data based in WGS84. Included in the CSV file is a variety of fields two of which are the lat and lon. The accompanying documentation makes no mention of the datum that was used for the coordinates. Is there a way to calculate it? If not, because it's US data, would it be safe to assume it's one based on NAD83?

I am going import this into a geography field in SQL Server 2012. I'm guessing that the SRID is either 4269 or 4326. I'd like to be able to determine which it is and transform it if necessary.

## 1 Answer

lat/lon can be either NAD83 (EPSG:4269) or NAD27 (EPSG:4267). WGS84 (EPSG:4326) is pretty much the same as NAD83.

You can easily check for some sample points which of the two you have.

The difference between the two is only about 40 to 100 metres.

• The NAD*** is only for North America just to clarify for non-NA folks
– user681
Aug 23, 2013 at 18:16
• Thanks for the distance difference. I noticed that the Helmert transformation between 4269 and 4326 were close, TOWGS84[1.0, 1.0, -1.0, 0.0, 0.0, 0.0, 0.0] but didn't know what that would translate to in distance. Aug 26, 2013 at 17:27
• I wonder if those parameters are correct. EPSG database lists about 10 parameters sets for NAD27 to WGS84 apart from NADCON. They discribe the shift of the center of the clarke1866 ellipsoid to the WGS84 ellipsoid. Aug 26, 2013 at 17:40