This issue has been solved. Trying to estimate the scale by taking
measurements on the paper maps failed despite every advantage that should have
maximized the precision of the measurements. A distance measured north-south
yielded a different scale than a distance measured east-west. Averages of ten
of each yielded different scales in these two orientations. The only thing I
can think of that would produce that result is that the image was distorted
differently in height than it was in width.
But the whole issue was resolved when Kinkos agreed to examine the process and
reprint the job. After one test panel, they told me they figured out what had
happened (although they didn't tell me what that was). They reprinted the big
panel and one small parcel map, and they line up perfectly just as I had
planned. They are in the process of reprinting the rest of the panels at no
cost to me. For long-story reasons I'm not inclined to share, I didn't think
they would do that. The rest of the work going forward is going to be SO much
simpler because of that.
Thank you all for your help!
- John A.
John,
Is it possible to ask Kinkos what scale they printed the base maps? They don't
have to actually reprint the maps, just go through the motions. Open the PDF
and look at the print options. As Andreas points out, the default is often
"Fit" and there will be a "zoom" or "scale" percent displayed in the
application (I use Foxit, and Adobe and both show this). The page size parcel
maps will have to be printed at this scale. If they can guarantee that the
print scale was 100%, then I would assume some other export discrepancy.
David
On 5/27/2021 4:15 AM, Andreas Neumann wrote:
Hi John,
No - the PDF export does not distort the scale. But the printing of the PDF
file might.
It is absolutely important that - when printing the PDF - the setting "Actual
size" or "Custom Scale at 100%" is used. All other options will change the
scale.
As far as I know, the default option when printing is "Fit", which will often
shrink the content by some percentage - because some often "invisible" or white
background might be present in the file that extends right to the edge of the
page format. Acrobat then thinks that the content goes beyond the "printable
area" of the printer and will scale down the whole file.
Hope that clarifies this potential pit-fall when printing PDF files. It might
well be a different issue than the one I describe, but this is a very common
source of error that I know.
Andreas
On 2021-05-27 10:02, John Antkowiak wrote:
Hi, Jochen. Your suggestion sounds do-able; I'll play around with it and
see if I can sort it out. I've got some digital calipers around here somewhere
:) What I'm hearing is that the process of converting both the base map (and
yes, I did create it in QGIS) and the parcel maps into PDF will distort the
scale. (And that a print shop might compound the problem by manually fitting
the source file to the printable area. Yes?) A question then is why didn't the
PDF conversion distort them all the same way, to the same degree? The base maps
are done now and I couldn't afford to do them again no matter what, so they are
what they are. Going forward, is there an export option in Print Layout that
will not distort the scale of the parcel maps? I am so relieved that someone
has an explanation for this! - John A. ----- Forwarded Message -----
From: [email protected] <[email protected]> To:
"[email protected]" <[email protected]> Sent: Thursday, May 27,
2021, 03:33:12 AM EDT Subject: Re: [Qgis-user] Did scale change outputting to
PDF? Hi John, as I understand it, you created the base map in QGIS. If
you use the measure tool in QGIS to get the distance between two distinct
features in the map (e.g. road intersections) and then measure the same
distance on the printed base map with a ruler, it should be possible to
calculate the scale. Maybe use two distances, one aligned more or less
horizontally and one vertically, to check if the scaling is proportional. As
Andreas pointed out, it is probably a problem with the settings when the PDF
was printed. In my experience it is a good idea to go to print shops usually
working for architects and engineers since they are familiar with the
importance of scaling (for advertising etc. it is more important that the whole
content is printed, so that scaling might be used to fit the output to the
printable area without potential cropping). You can print directly to a plotter
in QGIS if you have access to the device, avoiding the PDF detour. EPSG 2264
should be fine. Units should be US feet. Regards
Jochen Am 27.05.21 um 07:15 schrieb John Antkowiak:
Hi. This plan was too simple to fail - but it failed. The charity whose
project this is needed a large (that is... massive) paper wall map on which to
plot and rethink its delivery driver assignments. Both drivers and delivery
addresses are subject to change from week to week but it's not a pizza
delivery; this is a regular run to supply people in a bad way. So the plan was
to print the base map (roads and road names and county boundaries only) and
then print 8.5 x 11 address maps with parcel data and orthos. That way, the
base maps don't change but the physical parcel layer is flexible. (On top of
that is a third paper layer indicating which drivers go where so someone can
stand back and take in the whole picture graphically. Not a cutting-edge state
of the digital art solution, but not everyone is cut out for that. It is what
it is.) In order for this to work, the parcel maps have to be the same scale as
the base map. Which they were... in QGIS. We have to convert all the maps to
PDF to print them, and we had to send the base map PDFs to FedEx/Kinkos to
print the 9 map grid panels at 42" by 62" each. When we got the big base
maps up on the wall, we discovered the scale did not match the 8.5" x 11"
parcel maps output to PDF and printed from home. It's not off by a lot, but
it's enough to be painfully obvious from a single standard size sheet of paper.
I don't know how to reverse engineer the big map scale precisely enough to
enter a new scale number in the QGIS Print Layout. I didn't foresee it because
this never would've been a conceivable scenario at the engineering firm where I
picked up my meager GIS skills. (ArcMap sent a map directly to the plotter
without interim steps.) There was no scale bar on the map. It shouldn't have
been needed for this. Did something happen to the map scale when QGIS output
the map to PDF? Could the size of the image on the pdf page have been adjusted
manually or otherwise when being sent to a plotter with 42" paper? Could the
image have been distorted horizontally differently from vertically? For the
life of me, I cannot trial-and-error guess at a scale to enter. I've gone
through dozens of new 8.5" x 11" test maps trying to guess the correct scale.
Any ideas? Thank you all - John A.
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