12 GIS PRODUCT NEWS Time Awareness in ArcGIS 9.4 Leads to Better Understanding of Complex Geographies Visualizing Time in GIS In his First Law of Geography, noted geographer and cartographer Waldo Tobler states, “Everything is related to everything else, but near things are more related than distant things.” GIS professionals are well versed in visualization of spatial relationships and dependencies, of the proximity of near things and distant things, as in things you can measure with a ruler or with mile markers. But often when studying geography and looking for relationships and dependencies, equally important is proximity in time, as in something that can be measured with a watch or calendar. Pioneering environmental planner Ian McHarg is widely known in the GIS community as the “discoverer” of overlay theory, the base theory behind GIS. Another of McHarg’s discoveries—perhaps lesser known, but equally important—is chronology, or the placing of geographic layers in chronological sequence to show relationships, dependencies, and causation through time. “We found the earliest events, mainly of geological history, had pervasive and influential effects, not only on physiography, soils, and vegetation, but also on the availability of resources,” McHarg states, describing an environmental planning study in the 1960s, in A Quest for Life. He calls his discovery of chronology—the order or sequence of features through time—“. . . a most revelatory instrument for understanding the environment, diagnosing, and prescribing,” a construct that leads to a deeper understanding of structure and meaning in the landscape. Chronology is enabled by temporal data. Temporal data is data that specifically refers to times or dates. Temporal data may refer to discrete events, such as lightning strikes; moving objects, such as trains; or repeated observations, such as counts from traffic sensors. Depicting spatial change over time is a fourdimensional problem, and visualizing temporal phenomena on a two-dimensional map has You can control visualization of temporal data in ArcGIS 9.4 using the new “time slider.” always been a challenge. The simplest approach is the map series, where individual maps of geographic conditions at certain points in time are presented individually, in chronological order. Other inventive methods of visualizing change over time and space include creative symbolization, such as in Charles Joseph Minard’s famous map of Napoleon’s march across Russia. Temporal GIS is an emerging capability for integrating temporal data with location and attribute data, enabling temporal visualization and ultimately temporal analysis. Visualizing change on a computer screen in a GIS environment may give the viewer more options, but it is still a challenge. A simple yet highly effective method of visualizing time in GIS is through animation—displaying a series of maps in rapid succession on the screen. “The eye and brain are enormously efficient at detecting patterns and finding anomalies in maps and other visual displays,” says Michael Goodchild of the University of California, Santa Barbara. “GIS works best when the computer and the brain combine forces and when GIS is used to augment human intuition by manipulating and displaying data in ways that reveal things that would otherwise be invisible.” Building a robust temporal capability into GIS provides the human eye and brain with powerful visual tools to help determine the reasons why things happened in space-time. It is also key to modeling and predicting things that might happen in the future. ArcGIS Tracking Analyst 9.4 The ArcGIS Tracking Analyst extension provides specific rendering and real-time processing for change detection or “tracking”-style analysis on vector data. ArcGIS Tracking Analyst is ideally suited for applications that require near real-time processing of high-volume, low-latency information and when near realtime intelligence needs to be applied through actions or specific tracking-style visualization. New ArcGIS Tracking Analyst features at the 9.4 release include • A new storage mode that removes limitations on the size of available memory • New action types, such as E-Mail Alert, Data Modification Service, and Data Summary Service actions • New action triggers, including Arriving Trigger, Departing Trigger, and Track Crosses Trigger More Information For more information, visit www.esri.com/trackinganalyst. Charles Joseph Minard’s 1869 flow map of Napoleon’s 1812 Russian campaign is a classic example of spatiotemporal visualization (Image Source: Wikimedia Commons).