Webmap: Performance cost when data has different projection than basemap

[Martin1]

How much performance cost do I have to expect if the data I show on a webmap has a different projection than the basemap?

My data is in a local coordinate system while the basemap is in web mercator projection. In that case Mapviewer will re-project the data on the fly, so the data matches the coordinate system of the basemap. Does anyone have some information about the actual performance cost? The data I use is pretty heavy in some cases.

[berniejconnors]

Martin,

The draw times will really suffer if you are reproecting a lot of data on the fly.  I recommend you try it both ways.  Create a copy of your data and reproject it to Web Mercator.  Create two web maps, one with the data in the local coordinate system and a second with the data in Web Mercator.  See for yourself how much slower the web map is with the local coordinate system data on a Web Mercator basemap.

I had to do this myself about 8 years ago.  The performance was too slow in our local coordinate system.  I reprojected all of the data to Web Mercator.

However, today my solution is to use our own basemaps that also use our local coordinate system.  If you create your own basemap you don't have to use Web Mercator.

Bernie.

[Martin1]

Bernie,

Thanks a lot for sharing your experience here.
I did some benchmarking with two different webmaps which have basemaps with different projections (EPSG 3857 and 2056). Then I added the same (heavy) Map Image and Feature Layers to both and also a Raster (all EPSG 2056). I would have expected a performance difference, but strangely, the performance seems to be about the same. This is on ArcGIS Enterprise 10.8.1. Could it be that something has changed on ESRI side since 8 years ago.

I would prefer to use all our basemaps in our local projection (which is currently the case) but unfortunately,  some of the mobile apps like Survey123 do only work with Web Mercator (especially when the basemap needs to be downloadable when working in a disconnected environment). 

In case that you would like to take a look:

• Project on the Fly
• All CH1903+/LV95

Martin

[berniejconnors]

Martin,

        Is all of the data hosted on your own ArcGIS Enterprise Servers - including the basemap? When I did this 8 years ago I was using data hosted on my own ArcGIS Server combined with the ArcGIS Online World Topo basemap.  That might expalin the better performance you are getting.  Regardless, I would say the performance with reprojection on the fly is suitable.

        I did notice this in the Survey123 FAQ, It may be helpful:

"All basemaps used in the Survey123 field app must use the Web Mercator Auxiliary Sphere projection. Basemaps with other projections can only be used in the web app."

Bernie.

[Martin1]

Bernie,

Thank you for your input.
In fact all the data is coming from ArcGIS Server webservices. The ArcGIS Server is federated with our ArcGIS Enterprise, but the data for the webservices is not hosted in the Datastore but referenced from SDE (and other ) databases.
I think we will give it a try with reprojection on the fly.

Cheers,

Martin