The composite map gives a picture of the overall distribution, coloring each cell according to whichever answer is estimated to be most likely at that location. The more clearly one answer dominates, the darker the color. Individual maps show estimated probability of each particular answer at a given location, with larger probabilities shown in red and smaller probabilities shown in blue. At the moment, only the four most popular answers for each survey question are displayed.
The linked page shows the soda/pop/coke map; use the pull-down menu at the upper left (labeled “Question:”) to see the others. There’s a selection here. Only vaguely related, but I can’t resist passing it along: here‘s “Chaffinch Map of Scotland,” a poem by Edwin Morgan (quondam Poet Laureate of Glasgow and since 2004 Scottish National Poet) showing “the different names used in Scottish dialects for chaffinch, varying from chaffinch in the north over shielyfaw in the middle to britchie in the south.” As the site says, “a cleverly multilayered combination of poetry, cartography, ornithology, linguistics, and maybe just a hint of Scottish nationalism.”