Sometimes you only need one specific map. You do not need a full file replacement. You can edit the existing file on your phone.
Place the onlinemapsources.xml file into the customonlinemaps folder mentioned above. Oruxmaps Online Map Sources.xml
onlinemapsources.xml file is the "hidden key" to the OruxMaps universe, often described as a treasure map itself for outdoor enthusiasts. Because of licensing restrictions, the app cannot ship with pre-loaded access to many popular proprietary maps like Google Maps or specialized terrain layers. Instead, it provides this empty or minimal XML file that users must "populate" to unlock the app's full potential. Sometimes you only need one specific map
By default, the official map list is stored in the oruxmaps/mapfiles/ folder on your device's internal storage. Oruxmaps Online Map Sources.xml