I often get asked about the ability to redline within the ArcGIS Platform.Within the ArcGIS Platform there are essentially 4 options for Redlining as follows:
Create a feature layer for Redlining in the ArcGIS Platform.
These feature layers are essentially temporary layers. They can be replica of the primary feature layers being viewed in the client applications, so they have the same attributes, pick lists and behaviours. They though do not get entered directly into the feature class. This is the responsibility of the administrator to check the layers then use the ArcGIS Platform append tools to add them to existing feature layers.
Mark-up Layers.
Within Explorer for ArcGIS are Mark up Layers. These are essentially redline layers within explorer which can be share with the ArcGIS Platform. They can be added to Web Apps through the add data tool and viewed in ArcGIS Pro 2.0 or later. See the following for more information: https://doc.arcgis.com/en/explorer/ipad/help/markup.htm
Smart Sketching in Survey123
Within Survey123 is the ability to provide Smart Sketches. While not map based this is sketch linked to the location of the collection feature. The Following URL shows how this might be used https://community.esri.com/groups/survey123/blog/2017/10/09/smart-skething-in-survey123-stroke-by-stroke
Map Notes
Map Notes can be added to Map and edited within the Map Only. . It enables quick Mark-up of a Map for other to read and utilise. The following describes this further: http://enterprise.arcgis.com/en/portal/latest/use/map-notes.htm
Esri Australia Technical Blog 