[Qgis-user] Did scale change outputting to PDF?

[Andreas Neumann]

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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