JPEG print scale management

Andrew M's Avatar

Andrew M

04 Aug, 2019 04:36 PM

Hi all,

I am trying to print maps at 1:24,000 via JPEG format so I can add a legend and some info to the file after export from caltopo and before sending it to print.

However, when I print the jpeg, it is larger than 1:24k. When I print from caltopo, I set custom map size to 19x25" and tick the 1:24k ratio option, but when I go to print at 100% scaling, it ends up being closer to 26x50" and not 1:24k. Test file attached is a sample of a print jpeg at "100%/original file size"

Map of origin link https://caltopo.com/m/5HM3 under pro account at my email address.

When I use the identical print settings (19x25"; 1:24k; exact same layers, etc) with PDF format, it all prints perfectly.

Help! Do I just not know how to use JPEGs? Thanks yall

  1. 1 Posted by Andrew M on 04 Aug, 2019 04:39 PM

    Andrew M's Avatar

    Typo above. The jpegs I export from caltopo at 19x25/1:24k settings print to 36x50", not 26x50.

  2. Support Staff 2 Posted by matt on 05 Aug, 2019 03:06 AM

    matt's Avatar

    PDFs are built to real-world units, which is why they are great for printing - your computer knows that an 8.5x11 PDF is supposed to be 8.5x11. JPEG images are just a certain number of pixels with no real-world units, so there's no reason to expect them to print at exactly the right size.

    CalTopo PDFs are rendered at 200dpi; it sounds like your computer is trying to print the image at 100dpi, since your printed dimensions are double. But, I believe the JPEG image drops some of the border from the PDF, so while printing it at 50% would probably get you close, it won't be exact.

    If you actually want a map that's exactly 1:24k, and not just close to that resolution, you'd need to get a pro account, which lets you add corner images to the PDF (at 200dpi) that you can use for legends.

  3. 3 Posted by Andrew McAfee on 05 Aug, 2019 03:24 AM

    Andrew McAfee's Avatar

    Ok, awesome Matt, thanks. I have a pro account, and I will take a look at
    the corner image functionality. I am printing to jpg so I can easily
    include a small legend, as well as to state the contour interval of the
    quadrangle I'm printing and to state the adjacent quadrangles.

    I will also reach out to the print shop and see what resolution dpi they're
    using, and see if they can print a test map for me at 200dpi and the
    dimensions I need (19x25) and see if that gets me close enough to 1:24k for
    my needs. Otherwise it's back to pdfs! Thanks.

  4. System closed this discussion on 02 Oct, 2019 04:25 PM.

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