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#1
burwelbo

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It seems to me that most Cartographers rely heavily on public domain data for their cartographic projects. Since the data is captured at a particular time interval, I was wondering how important the currency of the data is? I assume for certain projects the cartographer would be required to collect or update existing data using aerial photographs and detailed field checking. So the question is how important is the temporal nature of data to most cartographic projects and what then is your methodology for cartographic production?

Bruce
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Saudi Aramco

#2
Martin Gamache

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From a base mapping perspective:

If the client is concerned with accuracy they will need to identify certain acurracy goals that need to be met in order for the project to be considered accomplished and thus the cartographer getting paid. This usually will be planned from the outset and costs for getting accurate data whether it be timely satellite imagery or new collection of imagery/vector will be factored into the scope of the project. It is the responsibility of the client to set those goals and the responsibility of the cartographer to meet them but also to make sure they can be met with the proposed methodology/data. You also need to outline how the accuracy will be measured. I've ben reading alot of litterature on forest mapping methods for the US forest service in California and they are quite explicit about what the accuracy needs to be and the methods for measuring it are well defined. That is one example where methodology, data, and accuracy assessment are well spelled out from the beginning, the way samples are collected, and where they are collected will affect the results.

If the client is relying on using old imagery/working from published sources and not paying for field checking then they must be willing to accept the limits of those sources. I suppose it is the cartographer's job to explain this to them. If you are your own client you have to decide what is acceptable/affordable based on your map's purpose and user requirements.

In an effort to cut costs cartographers use free or old data quite a bit and we rely on data captured by others. We may not do enough field checking if any. Most government source will document their accuracy requirements so you will at least know what you are getting from them. But when combining multiple datasets from multiple sources, with different errors, it is possible for those errors to multiply. Again this is something that needs to be understood by all parties involved.

On a map I recently posted I extensively relied on forest service data collected in the field with a GPS. Having not collected it myself I must trust it was collected correctly. However, when my client insisted that certain trails as mapped by the forest service with a GPS were incorrect I needed to edit them following his "recollection". Down the road as a publisher he will have to deal with these issues as his product's success will ride on its accuracy.


The question of scale is also to be considered.

An example comes from the world of orienteering mapping where not only are new vectors collected from new imagery for important maps (national competitions) they are also extensively and systematically field checked (as opposed to randomly sampled for alot of other maps) and continuosuly updated. For maps at 1:10,000 used by expert navigators (often mappers themselves) in highly competive races a misplaced or missing boulder or trail intersection is noticed and certainly commented on. On the other hand a city like Boston can go for years not updating its basic plannimetric data or having it's asessment base maps not aligned with the rest of its data and no one complains....

Insuring that, you as a cartographer, your client and your audience understands the data sources and how you used them goes a long way towards avoiding problems down the road. If you are mapping to a certain standard or specification, then you are responsible for ensuring you meet the standard and have the data to do so.

From a design perspective addressing this issue can take the form of good notes on your sources (including dates), and methods as well as a reliability diagram and detailed accuracy statements. Better to have an informed user then an angry user. Millitary maps often have these diagrams, they convey both the source of the data as well as the reliability. I really dislike maps intended for navigation that don't list any information about the map including the name of the cartographer. The more information the better. Sometimes you'll also see the "Not Intended For Navigation" warning....that is the ultimate "cover your a$$" disclaimer!

From a practical perspective Jensen provides a good introduction to accuracy assessment with a good list of further reading(Introductory Digital Image Processing Chap. 13). It is mostly geared towards remote sensing data but it is still agood place to start.

This is a great topic. Not sure if the design aspect is really covered in this rant but there is no real way to design around bad data. The old adage of Garbage In...garbage Out (GIGO) is very applicable.

#3
Derek Tonn

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As Martin has mentioned (GREAT reply, Martin!), the quality of the reference material going into a map design job is EVERYTHING related to the quality of the map that comes out. My firm is a different type of animal (no GIS, mostly campus mapping), but the same rules apply. We rarely begin a project without things such as a site plan, satellite imagery and oblique aerial photography....since we absolutely need those types of resources due to the fact that we do not actually visit 90-95 percent of the campuses that we are mapping.

Where we DO occasionally depart from accuracy though is when what is actually physically on a property makes it more difficult to navigate a property. For example, we often joke with our clients that we will need to "get out our virtual chain saw" and thin-out wooded areas in order for certain buildings to actually be seen. We also often have to "put a little make-up" on some of the buildings and grounds that we are developing...as nobody wants to see large patches of dead grass or a big, noisy air compressor sitting on the roof of a building. "Tie" always goes to accuracy, but there are some instances where a little more artistic license is called for.

Finally, the issue of scale will generally determine the level of accuracy for a piece. We tell clients that we could literally draw every brick on a building if they were willing to pay for it - :lol: - but a LOT of detail/accuracy is generally sacrificed in the name of budget limitations and our desire to avoid clutter in the finished imagery.

Not sure if this reply helps, but Martin's wonderful reply inspired me to try and throw my $0.02 in to the topic as well.

Derek
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#4
burwelbo

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Thanks for the replys.

I deal quite heavily with image data that is collected frequently and obviously rely on company data for mapping. But from an independent Cartographer and map publishing point of view, I would think this must be a big problem. Even available archived aerial photography could be several years out of date. So I guess you just give the client a number of options in your contract on the temporal aspects of the project. For example:

Option 1: Use existing publicly aquired/purchased data "as is" to produce results at this scale and date Price $$

Option 2: Purchase and process archived aerial photography to update public domain data Price $$$

Option 2: Contract aerial photography data acquisition or satellite image acquisition. Conduct detailed field survey Price $$$$

This could apply even to land cover I would think.

I would love to hear others comments on this, especially from cartographers that publish maps that they sell commercially.

Thanks
Bruce

#5
Hans van der Maarel

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One of the things I like to say is:

It's possible to make a bad map using good data. It's not possible to make a good map using bad data.

I think it's important to let a client know about the accuracy of the data that is being used to produce a map and what this will mean for the end-users.

One particular project that comes to mind is one I'm about to finish. It involves geocoding addresses (known contaminations and commercial properties for sale) and plotting them on Google Maps so that a user can select parcels that are for sale and potentially contaminated (my client offers cleanup services and management for these properties). The workflow is that an operator selects a contaminated property from a list, then sees that on Google Maps plus all properties for sale within a certain specified distance of it. He then reviews them one by one and tags the ones that are commercially interesting for him.

One of the questions I got was why I didn't show certain contaminanted properties. The reason was that the geocoding wasn't down to address level, but street, zip or city. Consequently, I could not be certain of it's exact location, or the distances to any properties in the area.

It's all about reliability. If you have data but you're not sure how accurate (both spatially and in time) and reliable it is, it's pretty much useless.

An additional comment (I had written this after Derek's post, but couldn't post it due to the site being down), I think you can express the relationship between cost, speed and quality in one of them triangular diagrams. Then it becomes clear you'll always have to make some sacrifices.
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#6
Kartograph

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All things said are very true for topographic mapping and GIS applications.
In the realm of thematic mapping things can be quite different.
Sometimes you are even asked to polish statistical data, or make them look more profound by making an InfoGraphic or map out of it.
A Historian for example, came to me and said: Show, how complicated things were with different ethnics at that time and place. Luckily for my conscience, things worked out without a polish. But he had ordered a map which shows how complicated things were and would not have accepted anything else. This happened a lot of times in the place I was working then, the "mission goal" of the map was stated. It was not the cartographer who took the data, decided on graphic presentation and presented the map to the scientist, who then gained insight into the locational patterns therein. The Insight was first and it had to be expressed.
Maps are not scrutinized as harshly as the statistical data itself. Thus in thematic cartography you have much more power in conveying a message, even if it is not backed up by the data.
In topo mapping, your customers will sooner or later know if your map is right. In thematic mapping, maybe nobody will ever even care to look after it.

It´s a bit like the saying: Everything said in Latin, sounds profound.

#7
Hans van der Maarel

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Sometimes you are even asked to polish statistical data


I had a teacher once who did that with our test scores... :angry:
Hans van der Maarel - Cartotalk Editor
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#8
frax

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Yep, I agree with Kartograph -- I see this thread as mostly referring to topographic/street/basemap. There is differences between cartography and cartography!

Thematic cartography often means presenting and communicating a body of knowledge (statistics, surveys, qualitative data etc), and is of course exteremly dependent on the data. But in this case, the principal investigator behind the data is someone else (that will take the big hit if there are data issues).
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#9
Martin Gamache

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My original response had a few paragraphs about thematic maps and demographic maps but then I removed them and decided to focus on plannimetric base mapping since it was easier and I believed that was the true nature of the original question. I would consider two categories of thematic maps, one with "hard" data such as census data that are collected using some described methodology and with some level of known accuracy and thematic maps that are purely subjective or based on the cartographer's interpretation of facts or events. I would then say that the rersposnibility for errors can lie in the data creators, the author of the map or the cartographer. These may be three different entities at times and the cartographer may just be assembling a map from flawed data compiled by an unethical researcher.

#10
Clark Geomatics

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Interesting post...

Ultimately, as the compiler / presenter of data, it would seem fair to say that the onus is on the cartographer to ensure your intended audience is aware of the limitations of the data used... liability, accuracy, timeliness, completeness, etc. - that is the real value of metadata.

As many of you know, it is often the case that a client drops off data that doesn't have any legacy - in our GIS projects, that type of data typically gets the boot or at least a big 'warning stamp'. Good, clean data costs money - it seems to be a fact of life.

GISers throw around the '75% Rule' - in a GIS project data conversion can easily cost 75% of the project - it's no surpise that metadata is a mandatory requirement when moving data around - it relieves a lot of headaches.

Cheers,

Jeff
Cheers,

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#11
Dennis McClendon

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I would love to hear others comments on this, especially from cartographers that publish maps that they sell commercially.


Unfortunately, there appears to be no market reward whatsoever for accuracy or timeliness in street mapping. At least in the US, the market only rewards having a large sales force. At the few places where buyers can compare competing maps, I suspect design counts for far more than accuracy.

I do street maps for phone books in the American West, a market in which I'm apparently the only vendor who does any fieldchecking. I regularly find something like 8-15 percent of what's shown on official government maps of the area to be incorrect or totally fictitious. I recently had a call from one of my clients who wanted to know why the competing book showed lots more streets in a suburban area than I did. I had to persuade him to drive out and take a look before he would be convinced that those streets--though platted sometime back in the 1970s--had never been built through the horse pastures. Obviously I can't compete on price with some guy who just pulls the streets out of the local GIS or out of TIGER. But I have meine Berufsehre!
Dennis McClendon, Chicago CartoGraphics
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