This is a simple web utility to open multiple Elden Ring maps at once in DSMapStudio and line them up properly. Use the textbox to search for maps by id or name, then press the Enter key to add it below. Also, click on related map ids to add them too. Designate one map as the origin map and get transform coordinates for others.
To transform a map in DSMapStudio, click on it in the list of maps while it is loaded. Then, in the Properties widget, enter the transform XYZ coordinates into the TransformNode "Position" field. Change Gizmos > Origin to "Bounding Box" to more easily manipulate parts in transformed maps.
See Elden Ring Map List for a full list of maps and an image of overworld map positions. This page and all of the data were created/collected by thefifthmatt.