Advantageously, layers upload together rather then individually without the length limitations involved in uploading directly to ArcGIS Online. Moreover, they retain their symbolization. They do not use up the limited storage allocated to a non-subscription ArcGIS Online account. And, critically for historical researchers, they retain their temporal functionality. When any of the time-enabled layers are turned on in the Webmap on ArcGIS Online, a time slider appears at the bottom of the map.
The biggest disadvantage is cost, of course. Servers and ArcGIS Server are expensive compared to using only a non-subscription ArcGIS Online account.
I constructed the Webmap for this post with my non-subscription ArcGIS Online account by using three of the layers from the non-temporal version of the same map posted at the end of April: (1) the number of deaths of enslaved Africans, (2) the density of those deaths, and (3) the place markers with their pop-ups. To those layers, I added three map services by using the Add Data button, selecting Search for Layers in a GIS Server, and typing in the address of the CADGIS server on which I had previously created the map services by uploading layers from ArcMap: (1) the voyage route lines, (2) the daily position points without being time enabled, (3) and a time-enabled version of the daily position points. The data for those layers remains on the server but is rendered as needed on the Webmap, similarly to the way the ArcGIS Online basemaps work.
I then embedded the Webmap below using the Share menu in ArcGIS Online. When I did that, I had turned on only the time-enabled layers for vessel daily noontime positions, set the time extent to 1751-1795, and the moving time window to 1 month. Lines of up to 31 points therefore snake around the Atlantic, one point for each sailing day in the month. Clicking the clock symbol in the top menu bar turns the time function on and off. Zooming in reveals the place markers and their pop-ups, date labels on the position symbols, vessel name labels on the route lines, and so on.
To access more functionality, such as turning layers on or off, users can click the link that appears below the map, which opens it in ArcGIS Online. There, users can see the list of layers and turn them on or off in order to, for example, display the sublayer of a single voyage of particular interest, set the time extent for the period of that vessel's voyage, and reduce the length of the time window. Users can also turn on the layers that show the number of deaths of enslaved Africans at a particular location on a specific voyage as well as the density of deaths across the breadth of the Middle Passage. For the layer called All Positions and Cargoes, which is not time enabled, clicking on points or lines brings up pop-ups with vessel information and links to the Trans-Atlantic Slave Trade Database records for those vessels, similarly to the non-temporal version of the same map posted at the end of April. The Middelburgs Welvaren's pop-up even has its image, taken from its logbook.
Note that sometimes the CADGIS server is down or slow to respond, so please be patient, try reloading the page, come back another day.... I am working on funding to acquire a new server and so on.
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