
148 Web Cartography: Map Design for Interactive and Mobile Devices
combinations found on Color Brewer (discussed and referenced in Chapter5),
never use hue to represent data on maps representing quantitative values.
Data Classification
Most choropleth maps classify data. Data classication is the process of ana-
lyzing the distribution of values in a dataset and grouping them based on
their location in a histogram. Each group is then assigned a color specica-
tion for representation on the map. Choropleth maps should typically have
between three and ve classes. In most cases, using more than ve classes
makes it nearly impossible for humans to ...