For line layers, simple line symbols are supported. If other symbols are used, the feature service converts them to a simple line symbol that best represents the original symbol. For example, a cartographic line symbol in the map document may be drawn as a simple solid line in a feature service client. If a line symbol is complex or has multiple layers, the feature service downgrades the line to best represent the original line symbol.
This may help.
My guess is that the symbol you're using the draw the lines in desktop is not supported when publishing the data to the web.
I could really use this for our sewer system lines as well. I know it's possible if you have your own server, so why can this not be implemented on AGOL hosted features?
It's a technical limitation. A feature layer (hosted or not) passes the feature geometry to the client app (browser, mobile device, desktop app) and the client draws it. Web browsers don't have the ability to draw complex line symbols.
This feature service has arrows on it:
I think it has something to do with being in a "map image layer", which if I understand correctly is only available if you have your own server.
Yes, map image layers are drawn by the server and return an image of the drawing to a client application. You do need your own server to host a map image layer.
oThis geonet thread gives info on how to symbolize properly:
Initially, I added specific service url's to the mxd from another published service.
I had this layer grouped in the mxd with another layer.
Published it using ArcGIS server as the host.
The symbology was ok in the rest end point viewer.
When I added the layer url to a web map on agol, it turned into a solid black line.
I tried adding the group parent url to the web map, but the web map shows an error:
The layer is not a supported type and cannot be added to the map.
Three possible solutions:
add the whole server url to the web map
Also, I attempted to remove the unnecessary layers from the web map, but it seems that once you add the MapServer url, you cannot remove the individual index layers of that map service.
Symbolize the line arrow by itself (NOT in a group layer, NOR any other layers in the mxd) in a source mxd.
Publish as a map service using ArcGIS server.
Add the Map service url (http://domain/arcgis/rest/services/SanitarySystem/ServiceName/MapServer) to web map
use any basic line symbol at the mxd, with color of choice, and no arrows.
use agol to accomplish arrow symbology
select a drawing style
2 pixels width
choose the arrow pointing to the right (third one down).