[Freegis-list] Cooperative mapping project proposal
Mon, 26 Mar 2001 18:07:08 +1000
Hi Brett, listers,
Apologies for the brevity. I'm looking at some similar issues at the moment.
Brett Matson wrote:
> Hi Adrian and everyone,
> Thanks for the great feedback. At the start of this project I had some long
> conversions with my thesis supervisor who raised some of the issues you
> pointed out. Others points hadn't occurred to me at all. I have outlined
> some of my thoughts on the points you made below. These are still just
> preliminary ideas that will hopefully provoke more discussion within the
> Free Software
> I will be using free, open source software exclusively throughout the
> I agree that the free web GIS software available is very good quality and I
> would like to further the free software/spatial data effort that is now very
> I have considered using ESRI shapefiles to store the data because it was
> difficult finding a format that could be easily read and written to by free
> software. This is why I decided that the Shapelib library, used in
> with the OpenMap package, would solve this problem. Do you know of any other
> data formats or libraries that might be more desirable.
I have just glanced at it (currently sitting on the coffee table along with a
year's worth of other reading ;-), however I am not sure as to its suitability
for data storage, as AFAIK it is designed as a transfer standard. There are C++
libraries freely available from the usgs site.
> Heterogenous Data Sources
> As you mentioned, this topic will require a lot of further consideration.
> Metadata will play an important part in attempting to solve this problem.
> Could you point me towards some of the metadata efforts you mentioned?
Also check out the ISO TC/211 web site for general info. Unfortunately most of
the info is restricted access.
> Disparate Dictionaries
> This is a good point. It seems that the simplest (but not most elegant)
> solution would be to restrict the number of classes available and allow
> the users who contribute the data to decide for themselves which class
> to use and then they could possibly provide additional information as
> metadata if necessary.
> I can't see how it would be possible to completely solve this problem
> in a system where people are free to add any data they like. Perhaps
> standards and guidelines could reduce the problem enough so that the
> map is still worthwhile.
> I guess a system where an unrestricted group of people collect data in
> their own way will always suffer from these problems. I wonder if simply
> attaching metadata that describes the travelling method, speed, position
> on the road, etc.. would be enough to cope with this problem?
> I like your idea for a data layer to demonstrate accuracy. Based on
> the results of the accuracy test, users could have a 'score'
> associated with their data providing other users with an indication
> of the quality of their data. Users could then improve their score
> by upgrading their technology or technique. By adding a temporal
> component to each data set, it could be recorded that in 1999 Jill's
> data wasn't too good but since November 2000 her data is very accurate.
> Users could then vie for the honour of obtaining the highest score
> or possibly have a top-ten contributors list.
> I don't know how idealistic this would be but its interesting thinking
> about the possibilities. Its this kind of user interaction that I hope
> would create a strong culture and inspire people to participate and
> have fun with it.
> A concern that my supervisor and I had was how these heavy restrictions
> and requirements would effect the culture of the user group. If
> people feel that there is a too strict regime placed on them,
> they may be less inclined to participate. An important aspect of this
> project is allowing people to use it freely, but as you pointed out, the
> map will be worthless if these issues can't be solved in a sensible way.
> Thanks again for your help, Adrian. If you have any more ideas I'll be
> glad to hear them. I would also like to hear the advice or opinions of
> anyone else interested in GIS or GPS. Even an expression of interest in
> using the system when it gets up and running would be a good motivator.
Brett, I would be interested in more detail about your plans - especially along
the metadata lines ;-) Maybe a co-operative approach? Maybe we could even get
AUSLIG interested in the open source approach :-)
> A website for the project should be up in the next couple of weeks which
> will provide more details.
> -----Original Message-----
> From: Adrian Custer [mailto:firstname.lastname@example.org]
> Sent: Monday, 26 March 2001 3:34 AM
> To: Brett home
> Cc: email@example.com
> Subject: Re: [Freegis-list] Cooperative mapping project proposal
> Hello Brett and "Free-GIS list",
> Your enthusiasm is to be appreciated so take these comments as response
> not criticism. Your goal is great, but there are a huge number of
> difficulties with what you are tryng to do.
> I won't address the technological difficulties except to encourage you
> to use a Free back end to your system. My understanding of web based GIS
> is that it is by far the most advance of free software GIS efforts and
> that, with a bit of work, you could actually have a whole Free gis
> system which is "web based". So, take a leap into the unknown and break
> out of the shadow of ESRI. :-)
> There are quite a few problems which emerge when future users attempt to
> assemble data from heterogenous data sources. Your end vision seems to
> be to have a huge amount of data which, although perhaps occaisonally
> conflicting, could be amalgamated into a decent gis data base. Most of
> the problems I see with the heterogenous origin of the data set are the
> problems addressed by the large METAdata efforts in GIS. You message
> shows you've thought about these data issues but I would encourage you
> to spell out early how to deal with this heterogenous data.
> Look from the perspective of your future users comming to get data from
> the system. Consider what they are able to say about the data, how they
> are able to assess quality and reliability of each data set. Then
> consider how they could resolve differences between data sets.
> As an example, I have submitted my data set of this tiny place in
> ethiopia. You have a back drop of say the Digital Chart of the World and
> a quick check shows that my elevations are resonable for that part of
> the world so the data is at least plausible. Now another user, has taken
> a trip to the area and submits her data. The same base check shows that
> the data is plausible so it's accepted. Now a user grabs the two data
> The data dictionaries will be different. How to decide what we both
> meant by roads. (I had four classes (major, minor, passable,
> walkable) The second user could have had a totally different
> description. Some folks are trying to come up with a standard data
> dictionary but I suspect they will fail because we don't all want
> the same information from the planet. You would have to think how to
> resolve disparate dictionaries (disparate definitions of data
> Did we move down the roads in a similar fashion? Who moved down the
> centerline, who stayed in their lanes? How fast did we move? Or did
> one person survey and another drive?
> I claim to have differentially corrected all my data. How do I prove
> to the next user that my data are accuarate? You should think about
> developing some data layer that would demonstrate accuracy. For
> instance you could require some of the data submitted to be a repeat
> visit to the same location ten days apart. A good metric like this
> would be really helpful. Consider the thematic information:
> You could of course punt and simply give the third user all the data and
> let them slog throught it making their own decisions. This doesn't help.
> You still have to figure out how to provide them with the information
> they will need to make these decisions. If you don't your whole system
> will just prove useless.
> So you are left with imposing some fairly heavy
> restrictions/requirements of data submitters for data compliance or
> meta-data inclusion or left with doing a lot of resolution, filtering
> work on your end. Either is practicable but you are going to have to do
> something to ensure some standardization of your data. It's tough and my
> personal take on this is that the data could never be well integrated
> into such a system unless you started out with that in mind (i.e. we all
> gathered data for the GNU atlas in GNU GPS format :-) )
> I also think that the quickest way to get a decent global data set is to
> force it out of the US goverment. They have some great global data sets
> that they are holding on to illegally (e.g. the Digital Chart of the
> World Level 1 (or 2?) ). thinking has become mostly that it's better to
> force the US government to release the data it gathers into the public
> domain as required by law
> This page is old but relevant:
> So good luck with your project and do consider some of these issues all
> the way through to the end user you have in mind.
> Freegis-list mailing list
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