Posts Tagged ‘Chrisman’

Like a Memory Lost in Time

Thursday, March 14th, 2013

Langran and Chrisman (1988) covered various conceptualizations of temporal GIS, stressing temporal topology and the need to visualize temporal structure, trap errors, and minimize data storage requirements. In a topic based on the conceptualization of abstract and multidimensional notions, it was enormously useful for the authors to include simple visualizations of the conceptualizations of time, especially in terms of temporal topology (i.e. how events are connected and related temporally).

One visualization of time that the authors ultimately reject as flawed in several ways is that of showing separate “scenes” or “states” in chronological order. I completely agree that this is a flawed practice primarily because of the hidden topological structure of the “states” (e.g. proof that one state occurred before or after another scene, and the interval between them). However, it is also the simplest for a layperson to understand. The authors drew the analogy of a motion picture, and that is significant because films function much as our own memories do, one scene at a time. We cannot capture events in time as anything other than isolated from one another. When we remember an event, we imagine a single image, followed by another and another if the memory is strong. Likewise, those images are from only one perspective—our own. I mention this as a slight digression only to draw a parallel to GIS. Even if we were to adopt the overlay or multi-polygon methods that the authors recommended, we would be ignoring the fact that mapping (at least traditional, top-down mapping) is drawn from a single perspective and that change, the manifestation of time, happens differently from any given perspective.

– JMonterey

Temporal geographic information: a work in progress

Friday, March 23rd, 2012

The importance of time in Geography has become more relevant for me as I began working on my research project. It was helpful to read Langran and Chrisman’s (1988) article. In a way I was comforted to relate to some of the issues with regards to dealing with time, but at the same time felt discomfort that these issues are still around. We live in a digital geographic world, as sah mentioned in their post. Andrew stated PPGIS and HCI display the issues that arise when using Google applications. Currently dealing with the LBS and open-source world where everything is rapidly changing, new versions of software quickly replacing the old, past problems quickly become obsolete. However, I have learned from this article that time, like other fundamental concepts in Geography, is different. It is still a timely (no pun intended) issue. So how do we go about dealing with mapping time, along with theme and location (1)? Although still in its early stages, the Ushahidi platform may fulfill the requirement of being “a temporal database that makes the time dimension accessible to users” in  the example give by the Ghana Waters initiative (2).

The space-time composite section reminded me of the problem of overlaying a polygon layer created in ArcMap. For example, a geographer decided to represent suburbs of a city by digitally drawing polygons. If they want to display this as a choropleth map, displaying crimes throughout the city, they can do so. However, over time, the boundaries of suburbs may change, thus a new layer must be created to ensure timely accuracy of the theme and space that is represented. I believe the advantage of having Google Earth now, as opposed to 1988, is that we can integrate conventional software databases like ArcGIS with user-friendly, interactive virtual globes to try and solve time related problems. Altering between suburb overlay choropleths from one time period to another can be done by checking a box. Creating a time-lapse animation could be a possible solution to static images that “do not represent the events that change one state to the next” (8). It’s still a work in progress, however, the less constraints we have when dealing with more philosophical and abstract concepts such as time (and ofcourse, ontologies), the better.

-henry miller