
130 Web Cartography: Map Design for Interactive and Mobile Devices
compared to one another. It is called perspective height because doing this
often gives the appearance of an oblique or tilted perspective even though
the data are being represented on a two-dimensional surface. Care should
be taken to avoid having symbols near the front of your visualization cover
symbols further behind. Also, this visual variable should never be used in a
three-dimensional (3D) globe-like interface (e.g., Google Earth), as compari-
sons between data are almost impossible to interpret due to the curvature of
Earth. Figure7.8 shows an example of perspective height ...