How do you deal with units and tiles?

I’m trying to get my head around the tile and unit system in little chunks. Unable to find a good resource on Google I thought I’d ask. The unit system is 100 pixel per unit, or 100m per unit? The issue I’m having is tiles should be units of 2, but if you use 24x24 you can’t fill a full unit. This is the same with all tile sizes that aren’t 10x10, 20x20, 100x100.

Why do people say to make tiles 24x24, 32x32, and so on? Doesn’t this make it an issue to map, considering there is always a lip over on the unit?

The best way to work with pixels is to establish a ratio of unit to pixel and stick to it.

As @Cherno and @AlwaysSunny explained you could have it be 16 pixels per unit of unity measurement but that is completely up to you, it just allows you to have a reasonably sized comparison between say two characters. It would look strange if one character had a unit-pixel ratio of 1unit:16pixels and the other has 1unit:32pixels. It might even make one character look as through it is further away and much larger, that is if you desire to use different PPU for the same visual space.

Of course this also helps with giving the user an understanding of depth. It is possible to use MORE pixels in the ratio for the background and will give the player the immediate understanding that the things with lots of pixels are far away and less is closer.

If you still want to affect PPU for different objects, use double the amount when describing foreground such that the world still seems coherent visually. Better for you to trial it and see if you can find a style that works for you.