Initial setting of camera and ppu to match playing table

Question

My goal is to implement another board game as close as possible as I would play it on a table - to not much think about how to arrange elements. The used space on table is in the dimensions of around 1x2m and most of my assets are scans of game cards with a touch of Photoshop (for personal use only). My question is regarding the camera, pixel on import of asset and converting to units. There are no physics in the game involved and it is 2D. For now it will be tailored to my own mobile but I would like to know if one way is preferred if I wanted to later change resolution or is just better best practice. From my understanding it would result both in the same outcomes but there might be some hidden trouble or side effects.

Should I (convert for myself to get a feel for dimensions) take 1 unit as 10cm -> scene of 10x20 units would represent my table or rather have a 1x2 unit scene (since most take one unit as one meter)
Assuming my scanned card has something like 2000x1000 pixel (and is 10x5cm big on a real table), does it make more sense to have it imported as 2000/20000 under pixel per unit or downscale the image first before importing it with a lesser value? I don't really care currently about build/ asset size.

DMGregory · Answer

Your choice of units within these ranges doesn't matter that much. The math all works out the same.
Usually units only start to be a problem if you're working exceptionally small (eg. 1 unit = 1 pixel) or exceptionally large (eg. 1 unit = 1 km).
Between metres and centimetres, there's not really enough of a magnitude gulf to be a problem, as long as you're close to the origin. So just use what you find comfortable.
Regarding the image size, it sounds like you already understand the trade-off you're making: import time and build size.
If you never plan to show the cards more than about 1000 pixels tall on a screen (filling the screen vertically at 1080p), the extra resolution doesn't really do anything for you, but if you're OK with larger build sizes / VRAM needs or longer import/build processes as the engine resamples the files down to your working sizes — or longer load times as the running game pulls in the whole texture and mip chain — then you can absolutely go either way.
I almost closed this question as opinion-based for these reasons, but hopefully sharing it as a answer makes it clearer why this is just a judgement call you'll need to make based on your own goals and preferred working style.

Initial setting of camera and ppu to match playing table

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