A common saying among geospatial analysts is: A map is outdated as soon as it's created. This saying reflects the fact that the Earth and everything on it are constantly changing. For most of the history of geospatial analysis and through most of this book, geospatial products are relatively static. Raw datasets are typically updated anywhere from a few months to a few years. The age of geospatial data in a map is referred to as data currency.
Data currency has traditionally not been the primary focus because of the time and expense needed to collect data. Web mapping, wireless cellular modems, and low-cost GPS antennas have changed that focus. It is now logistically feasible and even quite affordable to monitor a rapidly changing object or system and broadcast those changes to millions of people online. This change is revolutionizing geospatial technology...