Do I need to repoject a shapefile before importing into ArcGIS Online?

[CarinaLuo1]

Hi,

I know ArcGIS Online uses the WGS 1984 Web Mercator coordinate system as the default projected coordinate system, and it will re-project layers in different projections on the fly to its default projected coordinate system.

I'd like to import a shapefile which is in a different coordinate system (e.g., NAD 1983 17N), I was wondering whether I need to convert this to Web Mercator before uploading it to ArcGIS Online? So my question is, in general, does the coordinate system of data layer (shapefile, CSV.) has an effect on the accuracy of displaying layers in ArcGIS Online?

[JayantaPoddar]

NAD1983 and WGS_1984 shouldn't have too much difference in relative accuracy. If you ADD ITEM (shapefile) with NAD1983, it will transform on the fly, whereas if the datum is WGS 1984 (Web Mercator), the rendering could be little faster.

In case you want to publish the shapefile in its custom Spatial Reference, you could publish it from ArcGIS Desktop.

[XanderBakker · Accepted solution]

When you publish a Shapefile by adding it as a ZIP file to ArcGIS Online, it will be projected to WGS 1984 Web Mercator (Auxiliary Sphere) as described in this section:Publish hosted feature layers—ArcGIS Online Help | ArcGIS 

Some best practices and limitations for using shapefiles in ArcGIS Online can be found at the end of this page:

Shapefiles—ArcGIS Online Help | ArcGIS 

However, as jayanta.poddar  suggests, if you can publish the data from Desktop to ArcGIS Online, you will have less limitations.

[LancasterGIS]

I realize this is 4 years old at this point, but I do not believe this is correct. First off, the link to how features are published in AGOL gives no mention of whether data is transformed into WebMercator, or simply forced into WebMercator with a null transformation. In addition, if the data is transformed, there again is no mention of which transformation is applied. 

This is fairly simple to test - take a shapefile derived from the national survey points dataset - https://www.ngs.noaa.gov/cgi-bin/ds_county_sf.prl. This will be in EPSG:4152 GCS_North_American_1983_HARN. Upload this zip file directly to AGOL.

Take this same shapefile, extract it, load it into Arc* and transform it into WGS84 with the latest WGS84<>HARN transformation. Export this data as a shapefile again, zip it and load it into AGOL. The feature locations will not match.

Bottom line - if you want to control the transformations of your data, transform it first and then upload it to AGOL.