The use of a green blob to represent each store does help emphasize the virus-like spread of Wal-Mart over the 45 year period and is rather impressive to see that there are now over 3200 stores! I could never see Asda (which the Wal-Mart group also own) doing the same thing in the UK.
Wal-Mart's spread across the US landscape
I visited a Wal-Mart Superstore in New Hampshire around a year ago and must admit it was a rather spectacular store (unlike even the largest Sava-Centre). Almost like the largest supermarket, Halfords, Currys, PC World, Homebase, B&Q and John Lewis rolled into one. You could get absolutely anything in that place.
That is, however, everything except a kettle! Americans do not seem to understand what one of these are! Shame.