In the Spatial Portal Imagery web service page click on the three dots (…) on the right of an imagery layer to get the list of software clients in which you can open it, choose Open in Map Viewer.
This particular example shows a tile-cached Restricted basemap:
Alternatively, click on the title of the Imagery Layer to open the Item Details page and choose Open in Map Viewer.
In the Map Viewer click on Modify Map on the top right:
This enables you to edit the properties of the imagery layer by clicking on the three dots (…) beside the layer:
In a tile-cached imagery layer/service you are not able to extract individual projects in a Map Viewer, and you have fewer options in the dropdown menu. Unlike in ArcMap or ArcGIS Pro you cannot turn the tile-cache off in a Map Viewer. Tile_cached services are cached down to a scale of 1:1129 and beyond this scale it stops displaying, therefore add a dynamic service with the same projects to the web map to continue displaying the imagery beyond scale 1:1129.
See the difference in options available after adding a dynamic Time Series service via Add -> Search for Layer -> Filter -> Imagery Layers then to add the service to the Map:
From there you can go back to Details and Content and click on the layer and more options three dots (…) of the added Time Series layer:
Filtering out individual projects
The Filter option enables you to add expressions to filter out individual projects:
Copy (via the three dots) the same layer in the Contents pane and apply another filter to compare the two layers by switching them on and off. The Map Viewer does not have a Swipe tool. Nor is it possible to enable time on an Imagery Layer in a Map Viewer where time has not been enabled in the service itself.
Show Table opens the attribute table at the bottom of the map and offers additional options for selecting, viewing and filtering individual projects, such as Center on Selection and Display Selected Images On Map:
