especially when your display attribute is in ordinal format. For example, let’s say you have some data on housing starts within a state. Each city and town within the state can be shown as a bar that comes out at the viewer via a 3D effect at different heights depending on the number of housing starts recorded for that place in the past year. With enough data the map can almost start to take on a continuous surface look and feel, like an elevation model of housing starts. A more typical example would be something like using the population of major U.S. cities as the field for extrusion (see Figure 6.22). labelS