Here is one terrific map, courtesy of Ray Vella at Business Week.
This map works on two levels:
- The red and green dots provide strong visual cues to support the conclusion that Wi-Fi networks are being widely deployed across American cities, except in the mid-west
- The three shades of brown show the number of networks installed or planned in each state. Inclusion of such state-level information justifies the printing of state boundaries. Without plotting state-level information, state boundaries become chartjunk, as in the heat wave maps I previously discussed.
What's more, we can assimilate the city and state levels. For example, focusing on Texas, we see from the dark brown shade that it is a state with many networks, and then from the dots, we can see further where those networks are.
A few minor improvements can be made:
- Tell us the upper bound of the legend, name the legend: by changing 10+ to 10-X, the designer not only provides us another piece of data but also harmonizes the presentation with the other two categories. Besides, the legend needs a title
- Be more friendly to the color-blind: the red-green contrast should be avoided as much as possible. If a graphic designer is reading the blog, please tell us where we can find studies of color contrasts
- Use a softer national boundary: the solid black line sticks out against the soft background and it is the least important bit on the map
One would expect the choice of three shades of brown and the intervals used for each shade to be keyed to the frequency histrogram of the number of networks (shown right). The current division divides the 50 states into groups of 8, 16 and 26. Are there better divisions?
Finally, most readers will find the number of networks to be a dissatisfactory metric because more populous states will likely install more networks. A density measure such as networks per person or per household or per unit area would have been more telling.
Reference: "Wi-Fi Nation", Business Week, Aug 1 2005, p.12.