Projection changes when opening hosted feature service in ArcMap

[KristalWalsh]

Hi all! I've been slowly moving our private lands biologists to a Fields Maps-based data collection workflow but there are still some remnant pieces/parts that we have yet to integrate.  I have created a relational database in ArcPro and defined it to a custom projection matching that of our agency data, published to AGOL as a feature service. The staff use a web editor for data management in the office and can create and manage their own data. But our agency has to incorporate a desktop site assessment which utilizes an ArcMap plug-in and when the feature service is opened in ArcMap, the projection changes--- so areas are incorrect.

Does anyone know how to preserve the projection from AGOL to desktop? @AlixVezina is this something you might be able to help with? Or can you point me to the right person? The staff use specific templates to also create maps and I have to explore whether I can set this up in AGOL. They do not have access to Pro. Thank you very much for your input. Kristal

[AlixVezina]

Hi @KristalWalsh ,

I am not too familiar how projections work in ArcMap, having mostly used ArcGIS Pro in my GIS life.. 🙂

Perhaps these two resources may be useful: 

• Specifying a coordinate system—ArcMap | Documentation (arcgis.com)
• About editing data in a different projection (projecting on the fly)—ArcMap | Documentation (arcgis....

Otherwise, I would suggest posting your question in the ArcMap community: ArcMap - Esri Community and hopefully someone there will be able to point you in the right direction!

[KristalWalsh]

Thanks, @AlixVezina. 

[KristalWalsh · Accepted solution]

I'm replying to my own topic here, in case someone runs across this in the future. When publishing data to ArcGIS online from ArcPro with a defined projection, ESRI's default coordinate system Web Mercator takes over. I don't know of a way to preserve the "incoming", defined projection. I did correct for measurements of areas and lines using Arcade expressions in pop-ups. When our biologists opened the feature service from AGOL in desktop (I did not anticipate this part of their workflow), the geometry corrections were no  longer preserved and their measurements were wrong. So we are limiting any geometry measurement reporting to AGOL where Arcade expressions can be applied.