This is (part of) the Catalan Atlas, a world map created around 1400 A.D. ostensibly by Abraham Cresques, the preeminent mapmaker of the period.

Why am I posting about this on dev.to? Because I printed some of it, and it's awesome, and it's huge. Like massive. It's 36 inches high by 48 inches wide. Normal movie and concert posters are only 36 high by 24 wide, so that gives you an idea of how large I printed it. It's a really big poster.

Here's the backstory:

My girlfriend really likes the Catalan Atlas, in particular the story of this fellow here:

His name is Mansa Musa and he was a very rich king of Mali. Apparently the story is much cooler than that but I haven't read it yet and this is not a history lesson.

There is a maker space inside Central Library in Downtown Los Angeles called the Octavia Lab; they have all kinds of stuff like 3D printers and Adobe Suite, a large format printer, CNC, laser cutters and sewing machines and whatnot. And it's free to those of us with library cards. My target: The large format printer. It's an Epson with a 36 inch wide bed.

The source files:

I found some very large files on Wikimedia Commons by searching for Catalan Atlas.

The results are a bit disorganized as returned by the search, but by mousing over each page of the overall atlas, I was able to open a bunch of browser tabs that had the pages in the correct order. The Catalan Atlas originally consisted of six vellum leaves (each circa 64.5 by 50 cm [25.4 by 19.7 in]) folded vertically, painted in various colors including gold and silver. Age and wear split these down the middle, resulting in two tall, slim sheets. Based on the original dimensions, the original size of each "page" (as I will refer to them) would be 64.5cm by 24cm, or 25.4in by about 9.8in.

So to get the original size, I'd print them at approximately 10 inches wide. I'll use sheet six as a general reference, but all the pages have very large JPEG files of approximately the same size in pixels; that is 6,451 × 15,770 pixels.

Hmmm... okay, let's do some math. When printing images you want an absolute minimum of about 300dpi (dots per inch). Ever seen a flyer, photo or sign that just looked like crud? That's because someone who printed it didn't know what they were doing, and used a source image with a low dpi.

So, with a source image of ~6500 x ~15500 pixels, how large can we print it and still have the desired detail level?

6451 / 300 = 21.5
15770 / 300 = 52.56

So, we can print these images up to 21.5 inches wide, and 52.56 inches tall, and still have 300dpi resolution! Awesome! That's more than twice as large as the original vellum map!

Printing:

The lab has a limit of one 36 x 48 inch poster per day, so that's my canvas size. I opened photoshop and created a file with 36 high and 48 wide at 600dpi, for extra detail. I also made sure to set the image type as CMYK (for printing) rather than RGB which is for web.

I chose pages 5, 6 and 7 to print, based on the importance to my amour and the dimensions of my poster. As you can see, Mr. Musa Himself is in repose on the middle page.

I downloaded the largest JPEG for each page, and dropped each one into a new layer in photoshop. Resizing them and ordering them was a snap, and I made sure to keep the original aspect ratio of each one. There was a little bit of extra space left over, so I added a title in a gutter on the right side. The font is Trajan Pro.

I exported the file as a very large PNG (769.7mb!) at 600dpi and dropped it on my thumb drive. Lauren, the librarian who was on duty in the lab that day, worked with me to coax the Epson software into doing what we wanted, and the print came out beautifully!

Big thanks to Lauren and the Los Angeles Public Library for everything! This was a lot of fun and I'm happy to share it with you all.

For those of you who may be interested, here are the links to all the pages:

File:Catalan Atlas BNF, sheet 1.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 2.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 3.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 4.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 5.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 6.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 7.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 8.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 9.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 10.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 11.jpg - Wikimedia Commons
File:Catalan Atlas BNF, sheet 12.jpg - Wikimedia Commons