Who came up with the name "Manhattan distance" (for the distance between two points as measured by the sum of the horizontal and vertical distances, as opposed to the length of the straight line between them)?
I am capturing information from a comment as a starting point for a community wiki answer to which others can add earlier citations.
Harvey L. Garner and Jon S. Squire, "Iterative Circuit Computers", in Proceedings of the 1962 Workshop on Computer Organization, Baltimore, 1962, pp. 156-181. (Google scan). On page 165:
$W(p)$ is the number of distinct pairs of modules at Manhattan distance, $p$, and does not refer to the number of ways of connecting a pair of modules.
The paper is about a computer arranged as a two-dimensional grid of tiles, which explains the use of Manhattan distance. The term is not explained anywhere in the paper, so its use appears to have been well established by 1962.
By collating many overlapping snippets from Google's snippet view, I was able to extract the following quotation from a document dating to the same year that explains the term:
Rodolfo Gonzales and Sandra Palais, "A Path-Building Procedure for Iterative Circuit Computers", University of Michigan Information System Laboratory Technical Note, 1962. On page 22:
[...] two senses are to be followed when tracing the segments in each of the horizontal and vertical directions. This means that once the vertical and horizontal priorities are established, for example vertical down and horizontal to the right, all the path segments have to be traced in either of the two specified senses exclusively. It is to be noted that this restriction on the allowable class of paths has the advantage of eliminating the need for an algorithm capable of tracing a minimum length path, since all non-regressive paths have the same length when measured in terms of the number of segments needed to connect the modules. This method of measuring distance has been called "Manhattan distance."