In web map applications, the meaning of basemap sometimes differs from that in use for print maps; basemaps are the unchanging, often cached, layers of the map visualization that tend to appear behind the layers that support interaction. In our example, the basemap could be the georeferenced historical image, alone or with other layers.
You should consider using a public basemap service if one is suitable for your project. You can browse a selection of these in QGIS using the OpenLayers plugin.
Use a basemap service if the following conditions are fulfilled: