Here’s another important work of earlier date and so not well enough known today:
Atlas of the Early Christian World, by F. van der Meer and Christian Mohrmann, trans. Marry F. Hedlund and H. H. Rowley (London/Edinburgh: Thomas Nelson & Sons, 1958).
It is quite simply an incomparable work (to my knowledge). The most important and the unique material is the maps, 40 of them, plus the large maps on the inside covers. The unique feature of these maps is that they show the locations of churches and other important matters. Map 1, for example gives the locations of all churches of the first century referred to in ancient sources. As well, this particular map gives known Christian writings of this period, and their putative provenances. Map 2 is a color-coded display of the spread of Christianity by 300 CE, the various colors showing the estimated density of Christians in various areas of the Roman Empire. Map 4 shows the location of churches founded before the persecution by Diocletian (304 CE), Map 5 shows churches in the 2nd century, Map 7 churches in the 3rd century, and so on down through to ca. 600 CE. Map 15b shows early Christian monuments between Antioch and Beroea, Map 18 churches of the ancient Diocese of Egypt. And so on.
In addition to the maps, there are 150 pp. devoted to photos of a raft of ancient artifacts pertaining to early Christianity and its world with impressively detailed notes for each one. And the large format (the book is ca. 26 x 35 cm) means that the maps are easy to consult.
Used copies are available for what seems a relatively reasonable price. It’s too bad, however, that the volume was allowed to go out of print.