Thank you, Andreas - I thought there must be a PDF error.
I didn't use any tiling plugin but rather created my own polygon for that. 
Other than the scale issue, I'm very pleased with the print quality.
So if the scale error is proportional I should be able to eventually home in on 
the correct scale to use. That's promising, and I appreciate your letting me 
know. Thank you very much!
- John A.


   ----- Forwarded Message ----- From: Andreas Neumann <[email protected]>To: 
John Antkowiak <[email protected]>Cc: QGIS User List 
<[email protected]>Sent: Thursday, May 27, 2021, 02:27:20 AM 
EDTSubject: Re: [Qgis-user] Did scale change outputting to PDF?
 
Hi John,

A very common error when printing PDF maps (regardless of the software that 
generated the PDF), is that the print shop scales it down to fit the 
"printable" area. Then you end up at somewhere around 95% (plus / minus) a bit

The PDF viewers (at least the Acrobat one) has a setting to print at 100% (but 
this is not the default) - it has to be done consciously. However, this 
normally scales uniformly, not separately for width and height.

On the topic of "base maps":

Can you explain what source/mechanism for "base maps" you used? Are you 
refering to "tiled" maps, perhaps consumed through the OpenLayers plugin? This 
plugin is a known to be a source of error for misalignments and the plugin 
should be avoided. Even if you didn't use this plugin, I have to say that tiled 
base maps (e.g. consumed by the quick map services plugin or otherwise) are 
usually not suited for printing as their resolution is optimized for screen 
viewing. Printing these tiles would result in disappointing quality.

Greetings,

Andreas

On 2021-05-27 07:15, John Antkowiak wrote:

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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