EDIT - I now know that it is because uploaded CSV files with eastings and northings on the British National Grid datum still need to be geocoded, I guess since the main ArcGIS platform works in Lat/Lon. ArcGIS Online geocodes based on a free British National Grid geocoding service provided by ESRI UK.
My issue now is how would I replicate such a service behind a firewall given that my ArcGIS Enterprise system does not have internet access?
I have a vanilla installation of ArcGIS Enterprise 10.6, assembled with ArcGIS Enterprise Builder.
If I try and uploaded a CSV file to the ArcGIS Portal which has the data format "building_name, easting, northing," I get this message:
Your portal is not configured to find locations from address stored in files.
I believe this is because ArcGIS enterprise needs a geocoding service accessible and the default ArcGIS Online service is on the internet and we are behind a firewall, so it can't be accessed. Though in this case I have locations already and no addresses, so why is it prompting me to find locations from addresses when there are not any?
To summarise, my question is why do I need a geocoding service to host as a feature layer a data source that is already geocoded? (i.e. has Easting/Northing in a given projection EPSG:27700).
Unfortunately not, I still get an error message:
My understanding (after some more research) is that since these are British National Grid Eastings and Northings they need a lookup to translate them into whatever the ESRI Portal uses as its default mapping system.
Perhaps it is the terminology "address" that is confusing but it looks like If i feed this CSV into ArcGIS online it will use the "BNG Locator" which ESRI provides for free that translates the Easting, Northing or OS Map reference into...a location.... I guess it is in WGS84 Lat/Lon?
I suppose my issue now is figuring out how I can get "BNG Locator" functionality offline and behind a firewall since virtually all our data uses this projection.
Shot in the dark... but what happens if you publish a simple service that uses the British National Grid projection as the data frame projection, and then set that as the basemap for the web map viewer? I'm wondering if then it'll use eastings/northings instead of Lat/Long.
I imported one of our web mapping services running on EPSG27700 and ticked the "set as basemap" option when adding the layer. The data frame within the web map definitely changes since you can no longer use the measure coordinate tool (which would previously show Lat/Long) but I still get the same error message when trying to add a CSV with Eastings/Northings in BNG.