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When is a map (image) too large?

I am using three poster sized maps in my campaign. They are originally 21 inches by 32 inches each. I was able to convert them into jpeg files, so they don't use too much data, each map is about 4MB. In order for me to use the roll20 scale of 5 feet per grid, I had to make each map fit a grid of 160 units by 250 units. Each square or unit on the original map is a ten foot square. The grids from the maps into roll20 grids aren't perfectly fitted, but they work. I remember reading in an earlier post that large maps may cause lag of the game. "The maximum size limit for any single image is 5MB (10MB for paid accounts). Additionally, very large maps should (currently*) be avoided because they can cause lag with people's video cards. Divide a large map up into sections to prevent this. *The Devs have an update on the Development server which reduces the video card lag on large maps. The definition of a very large map varies but typically I would suggest keeping it to about 25x25 squares (or 1750x1750pixels) per map section." Are my three maps too large? If they are, please let me know as I don't want to get everything set up, then encounter lag while playing with other people. If you want, you (the Devs) can look at my maps and give me a second opinion (or advice). Please send me a Private Message and I'll let you know which campaign I am using the three maps in. Also, I read somewhere that "archiving" maps can help to ease lag. What happens when I archive a map? Am I just putting it in storage? Thank you for your help.
1413965311
Lithl
Pro
Sheet Author
API Scripter
I believe images larger than your screen size are already being broken up into multiple smaller images in memory, so your computer doesn't have to store the whole thing at once. Each user (player and GM both) is going to have to download your 4M image, but it shouldn't crash their browser or anything. At worst, they might have to wait before they can see the image. The VTT no longer tries to load a map until you try to view the map page. It used to load all maps that weren't archived, making archiving a useful tool for reducing lag on load, but now the load for map X only happens when you look at map X, so archiving it when you're not looking at it doesn't give you any gains. What archiving can do for you is help reduce clutter: if you're not going to use a map for a while, you can tuck it away and not have it take up any space on your page selection screen.
1413968609
Gauss
Forum Champion
The update occurred awhile back. Large images are divided up (without you being aware of it) so that your computer does not need to process the entire image. Could you supply the location of the quote so it can be corrected?
Thank you for clarifying that for me (and explaining about archiving). Yes, the quote was written by Gauss, October 5th (1 year ago) and was taken from the thread "Map alignment and you: or 101 ways to get your grids in a row".
1414015620
Gauss
Forum Champion
Ahhh, ok...so not on the wiki. :)
So does this mean I can proceed making maps from multiple images and also of tremendous size and not have any game-stopping issues?
1414024655
Gauss
Forum Champion
Gryfon, I will say...maybe? Each image on the screen requires processing power. Roll20 takes the really large ones and divides them up so you are not having to process the entire image at once. However, if you have many large images there may still be a slowdown. PNGs will also require more processing (compared to JPGs) so if you fill a map up with PNGs it may still slow your system down. Ultimately, try it and if you (or your players) have an issue you may have to back off a bit.
I've found, for size restraints (5M or 10M for supporters), that converting files from PNG to JPGs work well. Graphics might not be as high res, but overall functionality works.
I have several maps that are almost as large as you are talking about. The maps I'm using are 7-9M and I have them being displayed at about 125x125. There have been no problems at all with 5 players moving tokens around all at the same time.