They appear to be proposed British colonies that he considered while writing his book
Travels through the Interior Parts of North America, in the Years 1766, 1767 and 1768, first published in 1778.
From the
Appendix: "I have partitioned the country which lies adjacent to the eastern borders of the Mississippi into plantations or subordinate colonies; chusing such lands only for this purpose as by being contiguous to some river, might enjoy all the advantages I have before pointed out. These I have divided by dotted lines, and numbered; that future adventurers may readily, by referring to the map, chuse a commodious and advantageous situation. I shall also here give a concise description of each, beginning, according to the rule of geographers, with that which lies most to the north."
He then describes his proposed colonies № I. through XI. such as:
"№ VIII. This colony having the River Ouabache [Wabash] running through the centre of it, and the Ohio for its southern boundary, will enjoy the advantages of a free navigation. It extends about one hundred and forty miles from north to south, and one hundred and thirty from east to west."