“There’s just something hypnotic about maps.”
Not only are maps hypnotic, but they are also very practical. Simply, maps are our way of communicating where things are in relation to one another. When I say the word “map,” you probably think of a world map, but the earliest known maps are of the heavens. Dots on the walls of the Lascaux caves in southwest France date back to 16,500 B.C, and are interpreted to depict constellations: the position of stars in relation to one another.
There are many, many different types of maps. Architectural floor plans are also maps, as are dental charts and heat maps that show the location of pitches in a baseball game. What they all have in common is that at least one of their encodings is location in physical space.
In this chapter, we’ll focus on maps with two positional encodings: latitude and longitude, or more generally, x and y. Of course the earth is not actually a flat plane, so we will need to make use of what’s called a standard projection to avoid requiring a three-dimensional medium. There are many different types of projections, and Tableau uses the Web Mercator (sometimes referred to as EPSG 3857) projection common in online mapping applications such as Google Maps and Bing Maps.
One year before he died at the age of 89, French civil engineer Charles Joseph Minard left the world with a truly remarkable map depicting the ill-fated march of Napoleon’s army ...