You need to transform your data... here's what our resident coordinate system expert said:
Sounds like a classic missing-transformation problem! I checked a reprojection in ArcMap with and without a transformation it was around 135m. An appropriate transformation would be S_JTSK_To_WGS_1984_5 or S_JTSK_To_WGS_1984_3.
When shapefiles are uploaded and added to a web map, no transformation occurs. If, however, you have an ArcGIS Online subscription and publish from ArcGIS for Desktop, we do transform the data.
You need to transform your data... here's what our resident coordinate system expert said:
Sounds like a classic missing-transformation problem! I checked a reprojection in ArcMap with and without a transformation it was around 135m. An appropriate transformation would be S_JTSK_To_WGS_1984_5 or S_JTSK_To_WGS_1984_3.
When shapefiles are uploaded and added to a web map, no transformation occurs. If, however, you have an ArcGIS Online subscription and publish from ArcGIS for Desktop, we do transform the data.