How do I use custom projections?

04-22-2020 06:17 AM
Occasional Contributor III

I want to start using projections other than Web Mercator in my projects. I was really excited with this month's update,  Map Viewer Beta Update April 2020. So I'm trying to follow along two articles written by John Nelson, Enhanced Projection Support in ArcGIS Online and Here Are Some Equal Area Projected Maps for ArcGIS Online (and how to make them), but I am still unable to use the projections.

I know it has to do with tile layer that I have but I still do not understand. But according to John's post in Equal Area Projected Maps it states,

Layer Compatibility

Some notes about compatibility. You can add vector and raster layers to these maps. Raster tiles will render in them, too, but they may appear, you know, squished. Vector tile layers will not work in these maps because their differing vector projections will get into a pretty honorable sword fight and the basemap’s projection will emerge victorious and oust the upstart vector tile layer.

So if I'm reading it right it should work.

If I have the tile layer already placed in my map and then try to add one of John's basemaps I get this,

But, if I start with John's basemap and try to add the tile layer I get this,

Can someone please explain this to me? Thanks!

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3 Replies
Frequent Contributor II

From the screenshot forest ownership Minnesota layer looks to be a tile layer. If the tile layer does not match the same spatial reference of the basemap along with tiling scheme you wont be able to add it to a map.

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Occasional Contributor III

Yes, it is a tile layer. So when I publish the raster as a tile layer I have to publish it in the same spatial reference as the basemap I'm going to use in AGOL?

I guess I'm confused on the line "You can add vector and raster layers to these maps" when clearly I can't.

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Esri Regular Contributor

Hi Bryan, I think John was alluding to raster tile layers that also support export image (which enables them to be re-projected dynamically from the server). Esri raster basemaps support this, while hosted raster tile layers do not. Vector tile layers do not support this at all. 

Ultimately, any tile layers published in Online can only be added alongside other tile layers if they are in the same projection. It's fine that the projection is custom, just that all the tile layers in the map would need to have the same custom projection. The recent enhancements in map viewer Beta allow you to switch projections by adding tile layers with custom projections as the basemap and then building your map on top of the custom projection of the tile layer that was just added as the basemap (this is John's workflow basically). Previously, Map Viewer Beta would have prevented adding the tile layer as a basemap in this case.

Sorry for the confusion..we'll update the blog post to make it clearer.