Geohashing is something invented by Alan Munroe of xkcd fame. He published the comic below–although I don’t know when–with an algorithm on locating a place in a certain section of latitude/longitude. You take some input (in this case, the date and dow jones opening) and mash it together to get a decimal set of coordinates. If you don’t want to do the work, here is a map online that will do it for you.
Finished/Attempted geohashes