This map was published in 1863 in a paper by Wallace on the physical geography of the Malay Archipelago. It is the first map marking Wallace's line, here labelled as dividing the "Indo-Malay Region" from the "Austro-Malay Region". This line proposed by Wallace is the first ever deliberately-charted geographical division based on faunal differences between regions. His reasoning behind drawing a division between the groups of animals living in Asia and Australia at this location is described in an earlier paper "On the Zoological Geography of the Malay Archipelago" (1860). There, he discusses how groups of animals common in the northwest Malay islands are not found east of that line, while groups of animals common in Australia are not found west of it. His conclusion is firmly based in the observations he made while studying the species of the region. He wrote that "it is most striking to a naturalist" how groups of birds and mammals common in Java, Sumatra, and Borneo are present in Bali but completely absent in "Lombock," though the habitats of the islands are nearly identical and the waterway between them only 15 miles wide. His writing to support his placement of the line is full of specific descriptions of the ranges of different species; his studies of hundreds of species over the course of his travels enabled him to map out which groups of animals formed distinct faunas and locate the borders between those faunas. Since Wallace's line was first plotted on this map, it has been studied extensively up to today because where the faunas of Australia and Asia meet can inform scientists about the geologic history of the region and the evolutionary history of those animals.
