Posts Tagged ‘Temporal GIS’

TGIS back then…

Tuesday, December 2nd, 2014

From the Yuan’s article, he criticizes that the temporal GIS is not supporting properly the spatio-temporal modeling. He argues that the temporal database systems are being applied by time-stamping techniques to tables, attributes or values to incorporate time factor and therefore lack in proper application. I find this article interesting yet inappropriate.

This article is interesting in a sense that back in late 90’s, assuming from the range of dates of cited articles varies from late 80’s to mid 90’s, despite the lack of technologies that could have point out such problems in temporal GIS, yet he was able to pointed out and therefore one can only imagine the frustration when the methods were not appropriately applied and also the technology was not apt to well incorporate the temporal attribute as well at the time. Which leads to the reason why I call this article inappropriate, because it could have mislead to some people how temporal GIS is being not developed even today, whereas it is, at least in the perspective of technology, more than enough to be ready to be applied and being applied currently. It is all thanks to the advance in technology and crowd-sourcing. As Yuen have mentioned, “GIS will be more effective and precise by representing a fire, fire location, and how the fire spreads rather than burned areas at each point in time.” To relate to the example, nowadays, fire departments and natural scientists are closely monitoring the natural forest fire and the tracking, using temporal GIS. On the other hand, I find the burned areas at each point in time eventually leads to the evidences of fire spreads. However, it is facilitated by today’s technologies to create such connections whereas it was impossible to do so about 20 years ago. Hence, this article may be easily misleading or perhaps even confusing to people who are learning and being used to today’s GIScience technologies, especially without further information/background knowledge on TGIS.


Temporal GIS do we go back, or only forward?

Thursday, March 14th, 2013

Marceau et al.’s paper on temporal topology in GIS Databases outlines the faults with temporal GIS which seems echoes Marceau’s earlier paper on spatial GIS and its faults within social and natural sciences. In both temporal and spatial GIS, as I compare the two papers, the resolution seems to be one of the main issues affecting the accuracy of topology. To clarify, in spatial GIS, higher resolution reflects more data acquired and more accurate spatial topology; while in temporal GIS, higher resolution reflects a higher rate of sampling versus change in the area and more accurate temporal topology. To simplify, when dealing with temporal GIS, it comes down to the sample rate and what is included within the sample and thus, as talked about in spatial scale the “politics of scale”.

I believe that Marceau et al. tried to address the intervals of sampling, however I believe, from everything I have read on scale and scale changes, that Marceau et al.’s approach may be fatally flawed in that it is too simple to transfer to larger areas with greater variability of change. The method once upscaled will produce uncertainties if not greater uncertainties then what was already have within there study area. In essence, it is the “politics of scale”, were the question on how temporal GIS operates or can operate within a software platform, is mired in uncertainty by the data collected over time and the modification by Marceau et al. during the application of the data within a platform setting.

For temporal GIS, it may be impossible to go back in time to map. GIScience may have to start new from the present time working into the future. Therefore, GIScientists will know, now that platforms exist, that certain data sets need to be created that can represent the change rather then extrapolation into the past, which is inherently uncertain without wide-scale identifiers present (i.e. Land survey archeology or the process of digging into the ground to identify past land-uses for topology identifiers).



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

Temporal GIS an, Real-time, and Database System

Friday, March 23rd, 2012

For cartographic study, time has two meanings: one is the time that the event happened or lasted in the real world; while the other one is the time when the changes are recorded in the database system. Generally, the data collection should be started at the very moment that the event begins, and finished when the event ends. Temporal boundary, which is used to describe the temporal structure and separation of object versions, is also demonstrated in the paper of Langran et al. 1988.

For some real-time applications, the time difference between the event happen and the corresponding data is collected can cause problems, such as fire monitoring systems. If a fire disaster is detected but recorded several hours later, the lost will be unpredictable. Moreover, since database system is not designed in real-time, the event updates cannot be reflected in our GIS. Here are two challenges: first, how to record event in real-time as accuracy guarantee, and how to update the events in real-time with clear temporal boundary. Real-time technologies are integrated in temporal GIS, as a kind of solution to these two challenges.

In 2010, Mike Dana has given a very good presentation about real-time GIS database.

In their presentation, they present real-time ArcMap which can update and visualize the changes of geospatial information. By utilizing the real-time design, ArcMap can become a good platform for crisis command and mobile resource deployment.


Time after time

Thursday, March 22nd, 2012

In their post on temporality in GIS, Outdoor Addict brings up the date of the Langran and Chrisman paper–1988.  That was a long TIME ago!  So this brought to mind for me, the same as it appears to have for many others, that there must be many innovations since 1988 allowing us to better represent time in GIS datasets.  The sliders on internet graphics, or like in agent-based modelling, where the slider moves, changing the time step and the data displayed; the same thing in Google Earth, you can witness both historical changes and the visualization as day turns to night–all are examples of how temporality is displayed today: digitally.

But these are ways of displaying data, and as someone noted, not necessarily the best way of analyzing data.  This made me think further, though.  At each time step, the “event” is static in that time.  The process is fluid across time, but the events are solidly placed within time.  So my question is: why must we do time differently?  Couldn’t we have one map, where red dots are 1998, blue dots are 2000, and yellow dots 2012?  We could see where time factors in, and the data could be in one attribute table.

I am analyzing landscapes for another project, and we are comparing 1998 to 2004.  We have two maps with essentially the same parcels, and are trying to compare the land use.  We have one attribute table with all the parcels, and then have the time steps as individual fields, listing the land use at that time.  It can be displayed at whatever time step we like.  I can see where the authors suggest this is loading a lot of additional data, however.  If you have upwards of 20 000 unique attributes, say, but 75% of them weren’t changing, you would still have to store each time step of land use where nothing was changing.  But as the authors note, it seems the space-time composite is the best way to go forward, as combining all the temporal events in one space/data set minimizes the chances for error.

So at this point I’m not sure… where do we go from here?


“Take another picture! They added a fire hydrant!” and The Need to Go Digital

Thursday, March 22nd, 2012

Temporal GIS absolutely fascinated me once I found out what it was through this paper. The idea that spatial principles can be applied to time interests me as it signals to me that my spatial information knowledge has an additional use. The descriptions of each “image of cartographic time” were extremely helpful in visualizing precisely what the authors were trying to explain.

However, for each method of thinking about geographic temporality, events or mutations are needed. Langran and Chrisman describe a mutation as “an event that causes a new map state” and “a point that terminates [a] condition and begins the next”. It theory this makes sense. In the real world what qualifies as a mutation or event? Take for instance a map of a suburb’s development. The first version may only have a few houses. The next might have new houses, new streets and a new school and the following one might show a new fire hydrant as the only change. At what point in time does the map need to be updated? What event is considered significant enough to warrant making an update to the database? Additionally, who decides this? Perhaps it might be similar to the argument on ontologies as it could be a subject specific database where particular changes are more closely followed than others. A fire department may be far more interested in updates concerning each fire hydrant than a family which may be more concerned about where the nearest park is located. Furthermore, is technology advanced sufficiently to be able to determine this on its own once parameters are set or is this a manual job? (For example, could a satellite constantly taking pictures of the suburb be programmed to recognize when 5 new houses are completed and automatically update the database to which it is connected?)

On a slightly different note I would like to emphasize the importance of going digital for temporal GIS. The authors only point out that their work focuses on “digital methods of storing and manipulating sequent states of geographic information” but neglect to explain why this is so important. Much like geolibraries, the concepts and theory to operate and organize them may have been present may years ago (this paper dates to 1988 while geolibraries date to 1998) but the technology did not exist to bring them to the digital world and make them practical, useful tools and studies. For the many reasons discussed for promoting digital libraries in addition to the nature of spatiotemporal information, digital is the only way to move forward.

-Outdoor Addict