Geographic data represent spatial locations and non-spatial attributes measured at certain times. Goodchild (1992, p. 33) observes that "a spatial database has dual keys, allowing records to be accessed either by attributes or by locations." Dual keys are not unique to geographic data, but "the spatial key is distinct, as it allows operations to be defined which are not included in standard query languages." In the intervening years, software developers have created variations on SQL that incorporate spatial queries. The dynamic nature of geographic phenomena complicates the issue further, however. The need to pose spatio-temporal queries challenges geographic information scientists (GIScientists) to develop ever more sophisticated ways to represent geographic phenomena, thereby enabling analysts to interrogate their data in ever more sophisticated ways.