UCGIS Virtual Seminar - Fall 1998 [Back][Refresh][Options][Search] Questions for Scale White Paper [Edit*][Delete*] [Image] Questions Aaron Timbo 11/15/98 [Image] [Image] alternate sets of questions Nina Lam 11/16/98 [Image] [Image] Concrete example of Scale Bill Moseley 11/21/98 [Image] [Image] another example Ronald William Ward 11/23/98 [Image] [Image] Scale Problems in Byong-Woon Jun 11/22/98 Environmental Equity Analysis [Image] Scale in electronic data Blaine Hackett 11/17/98 [Image] [Image] Multi-scale Digital data Byong-Woon Jun 11/18/98 [Image] [Image] multi-scale representation Deana Pennington 11/18/98 [Image] [Image] Re: Multi-scale Byong-Woon Jun 11/18/98 Representation [Image] [Image] I disagree with you here Erik Shepard 11/20/98 Jun. Digital data are at the scale... [Image] [Image] Scale in Electronic Data James Nichols 11/18/98 [Image] Temporal Scale Bill Moseley 11/21/98 [Image] [Image] reply Peter Henschel 11/21/98 [Image] [Image] Temporal scale minh le duc 11/22/98 [Image] [Image] temporal scale and resolution Nina Lam 11/22/98 matters [Image] [Image] Nina, I apologize for E. Lynn Usery 12/02/98 entering this comment so late in th... [Image] [Image] scale Erik Shepard 12/03/98 [Image] [Image] Scale is a graphic E. Lynn Usery 12/09/98 concept and does not apply to digital dat... [Image] [Image] MAUP in Temporal Dimension Byong-Woon Jun 11/22/98 [Image] [Image] Scale vs. Resolution James Nichols 11/23/98 [Image] [Image] Re: Scale vs. Resolution Jason Seifert 11/24/98 [Image] [Image] Jim, Thanks for clarifying Bill Moseley 11/29/98 the difference between tempora... [Image] Fractal Analysis Guangxiang Cheng 11/22/98 [Image] knowing your scale Ronald William Ward 11/23/98 [Image] [Image] scale savy or scale oblivious Bill Moseley 12/01/98 [Image] [Image] comments Ronald William Ward 12/02/98 [Image] Scale effects and Data Availability Byong-Woon Jun 11/23/98 [Image] Another question Dawn Wright 11/23/98 [Image] [Image] Example of scale variance Nancy E. Wiens 11/24/98 within a data set. [Image] [Image] aerial photos Dawn Wright 11/24/98 [Image] [Image] re: aerial photos Jason Seifert 11/25/98 [Image] [Image] re:aerial photos Nancy E. Wiens 11/25/98 [Image] [Image] Ground Resolution will Nancy E. Wiens 11/26/98 vary in response to image scale. [Image] [Image] aerial photos Dawn Wright 11/25/98 [Image] [Image] The problem of scale Lumban-Tobing, Pago 11/27/98 variations due to terrain function with... [Image] [Image] I don't understand (in Carla Chenault 11/30/98 plain english for the non-expert) wha... [Image] [Image] question Carla Chenault 11/30/98 [Image] [Image] SLAR & SAR Jay Raiford 11/25/98 [Image] [Image] Scale variation minh le duc 11/26/98 [Image] Scale problems? Ronald William Ward 11/30/98 [Image] [Image] Scale independent databases Doug Albert 12/11/98 [Image] Post new message in this thread ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 15, 1998 09:14 AM Author: Aaron Timbo (timb0002@tc.umn.edu) Subject: Questions I will be leading our class review of the Scale white paper and have generated the following questions to help facilitate discussion. If anyone comes up with additional ideas they would be welcome. Thanks. Why is scale important? What avenues of research are being pursued by the UCGIS in terms of scale and scale effects? How does scale and its effects constrain spatial analysis? Why does scale,"constrain the detail with which information can be observed, represented, analyzed and communicated?" How do changes in scale or resolution affect classification and generalization? What are the implications of these effects? What is temporal scaling? Given your framework regarding temporal scaling, how might it affect analysis or representation of data? Why is it difficult to quantify the effects scale changes will have on analysis and representation of geographic phenomena? Why has the implementation of fractals or self-affine models been ineffective in compensating for scale change effects? Why has the widespread implementation of GIS's contributed to the scale problem? What complications may arise with the incorporation of coarse aggregate data and disaggregate data for spatial analysis of a geographic phenomena? Examples? Why have issues regarding scale become increasingly important to decision making and research? What might be some benefits of standardizing the connotations associated with the term "scale"? What are some examples of data loss associated with changes in scale? What is the relationship between ecological fallacy and effects of scale? How do the effects of scale complicate the conflation of data? How might cognition of scale affect decision making and understanding of geographic phenomena? Examples? (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2735) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 16, 1998 07:18 AM Author: Nina Lam (ganlam@lsu.edu) Subject: alternate sets of questions Thank you Aaron for providing such a comprehensive set of questions. I personally would be interested in hearing from all of you on the following: (1) Why scale is important? (i.e., what are the scale effects) Can you give some concrete examples based on your previous research or readings, for example, in different application areas (health risk assessment, transportation engineering, landscape ecology, socio-economic analysis, etc.) Every single simple example will help. (2) How should we realistically deal with the scale effects? Forget about it? Attach a warning statement? Simulation of scale effects? After going through Aaron's brain-storming questions, you will find these two questions easy. Nina Lam (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2742) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 21, 1998 12:14 PM Author: Bill Moseley (wmoseley@uga.edu) Subject: Concrete example of Scale As suggested by Dr. Lam, I write to give an example of scale in my own dissertation research. I am looking at the relationship between poverty and the environment in Africa. A common assumption has been that a) the poor are most affected by environmental degradation and b) that the poor are most likely to undertake actions that degrade the environment. Irrespective of whether or not this assumption is true, an interesting question becomes whether or not this assumption holds up at different scales. For example, is this true for rich and poor households within a village? Furthermore, is this true if we compare rich and poor villages, rich and poor ecological zones, rich and poor nations, etc. What do we do if the relationship changes as we change scales? I think the reality is that we often examine a relationship at a scale for which there is abundant data? We then go on to assume that this relationship holds true at multiple scales. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2949) ------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 23, 1998 07:12 AM Author: Ronald William Ward (ronward@arches.uga.edu) Subject: another example From the field of meteorology: In a quadrat analysis of the frequency tornados track along specific paths through central Illinois, quadrats spaced at a scale of approx. 1:10,000 showed no statistically significant pattern of tornado paths. In other words, the paths of tornados were random and could not be predicted. Using the same data, but with quadrats spaced at approx. 1:24,000, tornados were seen to travel along predictable paths. So which is it? Are tornado paths predictable or not? The answer is yes and no. At a larger map scale, or from the standpoint of a land owner, predicting whether or not a tornado will strike is not worth worrying about. But at a smaller map scale, and for regional disaster fund planners, tornados can be predicted to travel along the same general pathways over time, and smaller map scale areas can be prepared for the inevitability of a tornado. Both outcomes are scale dependent, and both outcomes generated significant pieces of information. Ron Ward (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2971) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 22, 1998 11:39 PM Author: Byong-Woon Jun (bwjun@arches.uga.edu) Subject: Scale Problems in Environmental Equity Analysis I'm working on a research paper which is looking at GIS-based environmental equity analysis in south eastern US. Several problems regarding scale and resolution in data are teasing me because multi-source, multi-scale and multi-resolution data in this research are used. The data are aggregated not only at multi-scales such as state, city and county levels, but also at multi-resolutions such as census tract, block group and zip-code district. Different combination of scale and resolution resulted in the variation in results. Diverse results would also result from different temporal scales. What scale is the most appropriate for this research? Is there any scale-independent method for environmental equity analysis? Is the multi-model for results a solution to deal with the scale effects? Jun (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2969) ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 17, 1998 05:12 PM Author: Blaine Hackett (hack0086@tc.umn.edu) Subject: Scale in electronic data I think Aaron has put forth some excellent questions. Our lecture will be dealing with these on Thursday. After that class I am sure we will have plenty to write about. I have another question I would like to pose to the group. While I was leading the class discussion on interoperability, we began discussing one aspect of scale in modern day electronic data. Dr. McMaster asked the class if electronic data has scale. At first I said that I thought it did have scale because it had to be input, whether through digitizing or some other method, from a map that was a certain scale. He then asked about satellite data? This stumped me. So I rethought my statement. Was I defining scale wrong when it comes to electronic maps? My thought was that if you digitize a 1:24,000 USGS quad, it is always going to be at a scale of 1:24,000. However, you can plot it at any scale. But that really isn't scale is it? It is more like accuracy. Since the input data was at 1: 24,000 it is impossible to get more detailed data of features as in the representation of a streams meander or road lanes. Therefore, it seems to me that the data is scaleless but only as accurate as at the scale it was entered. Any thoughts on this? (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2846) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 18, 1998 07:35 AM Author: Byong-Woon Jun (bwjun@arches.uga.edu) Subject: Multi-scale Digital data Basically, I agree with you, but I think the digital data are at multi-scales rather than scaleless. As you mentioned it, they can be represented in digital format at any scale even though the data are encoded into digital format at a certain scale. In this case, there are some problems with data content and accuracy as scale changes. For example, if the input data were at any large scale, they can be represented at any small scale through generalization and simplification methods. However, if the input data were at any small scale, the data content and accuracy remain questionable when they may be represented at any large scale because the digital data keep only as accurate as at the scale of the input data. That's why we need metadata including scale information. In order to solve this problem, it's about time to develop multi-scale representation methods for digital data. Jun. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2858) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 18, 1998 08:20 AM Author: Deana Pennington (penningtond@geo.orst.edu) Subject: multi-scale representation OK, now I'm confused! In your first statement, you say "digital data are at multi-scales," then your final statement is that we need to "develop multi-scale representation methods for digital data." I understand that digital data has multi-scales, and can be used at any scale smaller than that at which it was gathered. Could you please give me an example of what you mean by the last statement? What would be a multi-scale representation method? Deana (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2859) ------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 18, 1998 11:52 AM Author: Byong-Woon Jun (bwjun@arches.uga.edu) Subject: Re: Multi-scale Representation Well, I meant that multi-scale representation is a practical framework with which geographic phenomena are represented in optimal ways to support GIS data analysis and modeling across multiple scales. I think current GISs can not represent the geographic phenomena at truly multiple scales especially when we try to compare coarse aggregate data with less coarse data even though they can help integrate data regardless of scale differences. Some of primary issues in the white paper center around obtaining a good understanding of how to automate scale change and simultaneously represented data at multiple scales. GISs can be extened to provide users with intelligent automated generalization methods and optimal digital representations. Jun. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2878) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 20, 1998 11:17 AM Author: Erik Shepard (shepard@uga.edu) I disagree with you here Jun. Digital data are at the scale at which they were captured (e.g. 1:24000, etc). If you combine several layers at various scales, the resultant mosaic is then only accurate to the smallest scale (if you combine 1:24000 and 1:100000, any work you do on this combination is only accurate to 1:100000. I do believe that we need to address this problem, but without a great deal of redundancy, I don't see how. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2937) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 18, 1998 08:59 PM Author: James Nichols (jnichols@extension.umn.edu) Subject: Scale in Electronic Data I think one problem we run into relates to the methods we are using when we create a map from an electronic dataset at a different scale then it was gathered at, or when we combine information gathered at several different scales. There are generalization methods, some of which are "better" then others, and there are scale effects which are properties of features which need to be taken into consideration, both of these vary among classes of feature to some extent. The first, easiest it seems, step is to make sure that the appropriate metadata follows the data around and that there is lineage information. This gives an accurate picture of how a representation was arrived at, we can make some assessment of confidence in the results. The more robust, and much more complicated, method is to develop frameworks for multi-scale digital data as Jun suggests. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2896) ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 21, 1998 12:24 PM Author: Bill Moseley (wmoseley@uga.edu) Subject: Temporal Scale I am wondering if someone would be kind enough to clarify the meaning of temporal scale. For example, would scale in time refer to data that has been collected on an hourly basis, daily basis, yearly basis, etc?? Thanks! (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2950) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 21, 1998 01:56 PM Author: Peter Henschel (hens0045@tc.umn.edu) Subject: reply I think you are on the right track Bill. I think it does deal with hourly, monthly, yearly, etc. It may also deal with the year the data was collected. If two datasets were taken at different years it may effect the results. There is a problem of using data that is collected at different temporal scales. Data collected daily will be different from data collected yearly. Using two different datasets collected at different temporal scales may not give you the results you are looking for. A good question is how do we deal with data that is collected at different temporal scales? If I am wrong please correct me. Pete (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2952) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 22, 1998 10:55 PM Author: minh le duc (ducm@geo.orst.edu) Subject: Temporal scale Here is my thought about temporal scale in terms landscape ecology. The temporal scale heavily depends on the processes that you want to look at. If the inteval of the data you collected is longer than the interval of the processes occured you will miss the picture. For example, if the processes occered on monthly basis but data collected are yearly basis you will not able to characterize the processes. For the natural processes, sometimes we have to look at data for a long period of time, or in other words long temporal scale. For example, the equilibrium of an ecosystem changes every hundred years. That is temporal scale of the ecosystem's equilibrium. In order to characterize changes, we have to look at the data for at least more than hundred years or so. Because if we only look at the data for less than hundred years, we can not realize those chages. Let me know if I am wrong. Minh (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2968) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 22, 1998 09:25 AM Author: Nina Lam (ganlam@lsu.edu) Subject: temporal scale and resolution matters Bill and others: An example of temporal scale problem can be found in health assesment, not only referring to data collection, but the temporal interval for analysis. For disease with rare occurrence (cancers), it matters whether you should base your analysis on one-year, three-year, or any-year intervals. Moreover, we often encounter different medical data using different time intervals, how do we interpolate (or integrate) them is another important technical question that I am facing (not areal or spatial interpolation anymore, but temporal interpolation!) Regarding to the discussion on digital data and scale. I think we need to be aware of that even your map is based on a specific scale (1:24,000), different people may digitize the map at very different accuracy (resolution). It is very difficult to measure resolution, and the original scale becomes almost meaningless in the digital world -- resolution matters! In fact, I tried to make a point in my previous work that scale has many meanings, and resolution is part of scale -- measurement scale. Comments and suggestions? Nina Lam (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2956) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: December 02, 1998 07:53 AM Author: E. Lynn Usery (usery@uga.edu) Nina, I apologize for entering this comment so late in the process, but I think your statement about a 1:24,000-scale map which is digitized at different resolutions is problematic. The spatial data contained on the map has an ultimate limiting resolution based on the original scale. Regardless of the digitizing resolution (0.001 mm or 1 mm pixels), the original map contains the same information and that information is limited by the original scale. A coarse digitizing resolution may not capture all of the information from the map but however fine the resolution, a digitized version will never capture more information than the original scale permits. I agree with Bob mcMaster that digital data have no scale (rather than multiple scales), but all digital data have a limiting resolution, which with digitized maps is based on the original scale and with photographs and digital images is based on the camera characteristics, optics, flying height, film resolution and IFOV. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3089) ------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: December 03, 1998 06:19 AM Author: Erik Shepard (shepard@uga.edu) Subject: scale I don't know why, but I have a problem with this idea. It seems to me that digital data would have a scale equal to the scale at which they were captured (although I do completely agree with the idea of a limiting resolution). I'm not sure that I understand why you say that digital data are scaleless. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3111) -------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*] [Delete*] Date: December 09, 1998 07:16 AM Author: E. Lynn Usery (usery@uga.edu) Scale is a graphic concept and does not apply to digital data. Resolution applies to digital data and as I indicated depends on the source of the data. If the original source is a paper copy map or photo, then the limiting resolution is based on that scale. However, the actual resolution of the digital data will depend on the scanning or digitizing resolution. The concept in essence is that digital data are numbers. Scale requires a ratio (map distance to ground distance) and since digital data contain no ratio information, only a set of digital numbers, the concept of scale cannot apply. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3201) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 22, 1998 10:18 PM Author: Byong-Woon Jun (bwjun@arches.uga.edu) Subject: MAUP in Temporal Dimension The impact of scale on geographical research has been an indispensable issue as GIS has begun to expand into spatial analysis where multiscale data are frequently used and data integration is especially a problem for geographers because information synthesis is at the very heart of the discipline. Several issues related to scale problem have been identified in previous research. One of these issues is the modifiable areal unit problem (MAUP). However, most of studies have by far focused on spatial or geographical scale. It's about time to expand MAUP into temporal dimension in order to develop more robost theories in geographical research. Jun (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2967) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 23, 1998 03:43 PM Author: James Nichols (jnichols@extension.umn.edu) Subject: Scale vs. Resolution I think there tends to be confusion between what is temporal scale and what is temporal resolution. Here is my shot at it... If you had information that was gathered at yearly intervals over a period of ten years, then your temporal resolution would be 1 year and your temporal scale would be 10 years. Right? (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2981) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 24, 1998 07:33 AM Author: Jason Seifert (seifert@nws.gov) Subject: Re: Scale vs. Resolution Jim, That is my understanding of temporal scale as well. I am not sure that interpretation is valid for all circumstances though. Lets examine information gathered about a continuous process (ie river flow) at a 1 year interval for a period of ten years. Compare that to information gathered about an event process (ie lightning strikes) at a 1 year interval for a period of ten years. My understanding is that the river flow information would have temporal resolution of 1 year and temporal scale of 10 years. I contend that the lightning strike information would have temporal resolution of 1 year and temporal scale of 1 year as well. They strike (sorry about the verbage) me as having different temporal behavior. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2988) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 29, 1998 06:01 PM Author: Bill Moseley (wmoseley@uga.edu) Jim, Thanks for clarifying the difference between temporal scale and temporal resolution. Bill (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3046) ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 22, 1998 08:16 PM Author: Guangxiang Cheng (gcheng1@tiger.lsu.edu) Subject: Fractal Analysis After reading the artical of "On the issues of Scale, Resolution, and Fractal Analysis in the Mapping Sciences" (Nina Sir-Ngan Lam, Louisiana State University; Dale A. Quattochi NASA Science and Technology Laboratory, Stennis Space Center", I try to answer Dr. Lam's two questions. 1. Why scale is important? Scale is important because the variation of scale is often concerned in many fields. In the area of transportation which is my major area, different scales are needed for the same area for research purpose. The transportation network need a large scale while the study of a interchange needs a quite small scale. It is impossible to study these two together with the same scale. 2. How should we realistically deal with the scale effects? I think fractal modal may be a good way to solve the scale problem. Using the D value - Dimensionality = log (number of copies) / log (reduction factor) to measure different resolutions may be apppropriate. However, due to the non-linearity of geographic properties, the algorithm of D value is still not well developed. The geo-statistics may be the way to achieve that. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2966) ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 23, 1998 07:32 AM Author: Ronald William Ward (ronward@arches.uga.edu) Subject: knowing your scale I'm reading a lot of concerns about analysis outcomes being influenced by the scale at which the analysis was conducted. For geographers, changing outcomes and problems such as spatial autocorrelation are nothing new. In the geographic literature, and for research conducted in both human and physical sciences, often times (but maybe not often enough)scale resolution is stated explicitly along with reasons a particular scale of analysis was chosen. In other disciplines utilizing spatial data, as observed by some of the discussion participants, data are obtained at whatever scale they are available. When spatial data are collected from the field, often the scales at which these data are collected are chosen for the sake of convenience rather than any analytical consideration. In terms of the ecological literature, one rarely sees an explicit discussion of scale or the reasons behind choosing a particular scale for researching any particular ecological phenomenon. Understandably, in that the technology for smooth transition from one scale to another does not yet exist, and given the costs of collecting in situ data at multiple scales, few researches ever explore scale effects with regard to their research. This is why choosing the proper scale, at which to analyze any particular human or physical phenomenon, a priori is so important. Part of the UCGIS White Paper calls attention to the multidisciplinary nature of scale issues, and a research priority could be established to try and standardize consideration of scale issues between geography and other disciplines. Especially regarding policy formulation, policly makers should be made better aware of scale issues entailed in the spatial analysis reports they base their policies on. Ron Ward (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2972) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: December 01, 1998 03:48 PM Author: Bill Moseley (wmoseley@uga.edu) Subject: scale savy or scale oblivious Ron: I often wonder if policy analysts are unaware of scale or simply choose the results of analysis at a scale that conforms with their political agenda? Bill (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3078) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: December 02, 1998 08:04 AM Author: Ronald William Ward (ronward@arches.uga.edu) Subject: comments Bill, As is the case with statistical analysis and spatial analysis, scale considerations can be manipulated to show whatever it is you are bent on showing. So, I suppose scale issues are the same that way - bias is always a possibility. I don't doubt that policy makers with one political bent or another do this. My hope would be that there are some policy analyists outthere that are aware of the ways in which scale can be manipulated to achieve political policy ends - and when these sorts of scale manipulations are identified they are critiqued as such. Most agencies have policy analyists, research analysists, and data analyists in place. One of our graduates (Matt Kales) now works for the Georgia Conservency and his position there is just this - sort through the environmental policy proposals to assess if there is any bias or faulty statistics in the backgroud research. I guess what I'm saying is that if policy goes through the proper review processes, then bias can be identified. Certainly this is not always the case with every policy. kazi taiyari, Ron Ward (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3090) ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 23, 1998 09:31 AM Author: Byong-Woon Jun (bwjun@arches.uga.edu) Subject: Scale effects and Data Availability Currently, GISs facilitate to use multi-source, multi-scale, and multi-resolution data in our research. Thus, data availability have been another important issue. Even though we have a wonderful idea, we cannot do our research without data collection. If we have data for our research at single scale and resolution because of cost and data availability, is there any scale effect on analysis and modeling? Jun (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2973) ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 23, 1998 09:50 PM Author: Dawn Wright (dawn@dusk.geo.orst.edu) Subject: Another question The white paper talks about scale varying between data sets. What about spatial AND temporal variations in scale within data sets? Comments? Examples? Dawn (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=2984) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 24, 1998 10:08 PM Author: Nancy E. Wiens (newiens@concentric.net) Subject: Example of scale variance within a data set. I think an example of scale variation within a data set would be a data set whose origin is aerial photos. Completely level ground would have the same scale throughout, but hilly ground would vary with its actual distance from the cameras. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3013) ------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 24, 1998 10:15 PM Author: Dawn Wright (dawn@dusk.geo.orst.edu) Subject: aerial photos > I think an example of scale variation within a > data set would be a data set whose origin is > aerial photos. Completely level ground would > have the same scale throughout, but hilly ground > would vary with its actual distance from the > cameras. Good example Nancy! But let me play devil's advocate. Does your example refer to scale... or resolution?? :-) (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3014) ------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 25, 1998 07:01 AM Author: Jason Seifert (seifert@nws.gov) Subject: re: aerial photos That sounds like a trick question. The scale of an aerial photo varies as a function of terrain elevation. Ground resolution will vary in response to image scale. The scale and resolution of an aerial photograph varies throughout the image. These variables (and others) make it difficult to generate accurate measurements from remotely sensed data. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3019) -------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*] [Delete*] Date: November 25, 1998 09:09 PM Author: Nancy E. Wiens (newiens@concentric.net) Subject: re:aerial photos Jason, would you talk more about "Ground resolution will vary in response to image scale"? Nancy (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3020) --------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*] [Delete*] Date: November 26, 1998 05:44 AM Author: Nancy E. Wiens (newiens@concentric.net) Subject: Ground Resolution will vary in response to image scale. "Concurrently resolution may vary with image scale with acoustic vehicles OR with photographic vehicles it may vary depending on the strength of a camera lens on the vehicle (which we can vary in real-time as we're "flying" the vehicle over the ocean floor." Thank you, Dawn. That gave me the explanation I was looking for. Nancy (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3022) -------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*] [Delete*] Date: November 25, 1998 09:17 PM Author: Dawn Wright (dawn@dusk.geo.orst.edu) Subject: aerial photos > That sounds like a trick question. The scale of > an aerial photo varies as a function of terrain > elevation. Ground resolution will vary in > response to image scale. The scale and > resolution of an aerial photograph varies > throughout the image. These variables (and > others) make it difficult to generate accurate > measurements from remotely sensed data. Good response. We have a similar challenge when making "aerial photos" of the ocean floor with acoustic and photographic vehicles. With these the scale will change with water depth (e.g., the swath width of an acoustic vehicle will narrow as the depth shallows). Concurrently resolution may vary with image scale with acoustic vehicles OR with photographic vehicles it may vary depending on the strength of a camera lens on the vehicle (which we can vary in real-time as we're "flying" the vehicle over the ocean floor. Happy Thanksgiving! Deepsea Dawn (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3021) -------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*] [Delete*] Date: November 27, 1998 01:48 PM Author: Lumban-Tobing, Pago (lumbantp@ucs.orst.edu) The problem of scale variations due to terrain function within a single aerial photo can be solved by using ortho-photos. Ortho-photos are made by digitizing regular aerial photos with a camera that can move vertically to mimick the terrain variations, such that each point will be at the same distance from the camera. By doing so, each point within the image will have the same scale and any measurements will have the same accuracy. Ortho photos have been the primary data source for photogrammetry. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3031) --------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*] [Delete*] Date: November 30, 1998 10:56 PM Author: Carla Chenault (cchenaul@oce.orst.edu) I don't understand (in plain english for the non-expert) what an ortho photo is. I realize it is a modified image, but it seems this would be less accurate in terms of scale. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3059) --------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*] [Delete*] Date: November 30, 1998 11:00 PM Author: Carla Chenault (cchenaul@oce.orst.edu) Subject: question I don't understand (in plain english for the non-expert) what an ortho photo is or what it is used for. I realize it is a modified image, but it seems this would be less accurate with respect to scale. (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3060) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 25, 1998 06:17 AM Author: Jay Raiford (jraifor@lsu.edu) Subject: SLAR & SAR Very similar to Nancy's response but seems these two radars would also have scale variation within the image. In the near range there would be a small change and a large difference in the far range in scale and resolution. Right? (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3017) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 26, 1998 08:03 PM Author: minh le duc (ducm@geo.orst.edu) Subject: Scale variation My example is about biodiversity data. Let say we have data set of species in the same resolution for the whole United States. But the scale used for the nation wide analyses would be different from the scale used for state wide analyses. Because reducing the scale can increase the dominance of the contiguous classes, but decrease the amount of small and scattered classes in the presentation (Turner et al. 1989). And the temporal scale variation would be similar. My question is: How cenlular automata concept can be used to deal with the scale problem? (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3029) ------------------------------------------------------------------------ [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: November 30, 1998 08:05 AM Author: Ronald William Ward (ronward@arches.uga.edu) Subject: Scale problems? I don't know...a lot of what I'm reading here is that working in multiple scales is a problem because of technological limitations. The technologically enclined will solve these problems and working in multiple scales of time and space will become the norm. We'll all learn the technology, but we'll still be left with the task of deciding which scale to use for particular research. What I'm reading with regard to choosing a scale for research is 'be careful' because of scale effects. But if we are familiar with our topic, and have a good sense for the scale of best representation for our topic, then scale is not a problem, but a positive aspect of what it is we are researching. As a geographer, I wouldn't want a computer choosing an appropriate scale for me. This is rather like performing a statistical analysis. It's best to choose an analysis routine based on the research topic, the questions therein, and a little intuition. Ron Ward (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3053) ----------------------------------------------------------------------- [Top][Previous][Next][Print][Reply][Edit*][Move*][Delete*] Date: December 11, 1998 08:24 AM Author: Doug Albert (dalbert.unix1.sncc.lsu.edu) Subject: Scale independent databases J. C. Muller in "Generalizations of Spatial Databases" looks at scale independent databases that would be able "to produce cartographic representations at multiple scales from one single source of data". (Muller 1991: 25) Does anyone know more on this topic? (http://forums.library.orst.edu/forums/Index.cfm?CFApp=7&Message_ID=3238)