The Last Section (For now!) We will now explain about overall spread and what to look out regarding it.
How to look after spread issues
Spread issues happen fairly often within mapsets especially those who are fairly still learning or more around semi-experienced.
But what would be considered a spread issue? Well, usually a spread issue is when the gap is so big that you are essentially gimping a part of the player base with a difficulty within the spread for major cases, while minor cases it's usually when the difficulty is on edge and being simply nerfed down to solve the issue at hand.
Whilst this explains it pretty well there is a lot of other things to consider upon spread:
The length of the song
With spread rules and length there is at times were the mapper doesn't really need to map as many difficulties.
3:30 or higher the Mapper only needs to make a Hard or Higher.
at 4:15 or higher the Mapper only needs to make an Insane or Higher.
Anything over 5 minutes, the Mapper doesn't have a spread limitation and can choose to map what they please (as long as it is reasonable of ranking.)
What does this mean? It means let's say for example there is a mapset that is 4:15 or longer the 2 difficulties it has is an Insane and a Normal.
If you look at that and the mapper is going for rank, you might think "wow this spread gap is too huge to be considered rankable" But... it is. If the Insane is mapped as what would be considered as Low difficulty Insane (case by case), then the Normal is fairly optional and doesn't even have to be mapped.
As long as the Normal is good and rankable (so still have to follow the Normal ranking criteria and all), then things should be fairly okay for the mapper to rank and you do not need to point this out within a mapset.
Rhythm Density/Spacing overall within all difficulties
For this, you will need to look at all difficulties (or just the 2 that you will likely be comparing) to fully do this step. Since Star rating (SR) is usually a bad metric to go by this alone when determining when a spread is off as it isn't fully accurate as much as the difficulty Density/Spacing will ever be.
For Example, let say that at 180 bpm you have a Normal and a Hard.
The Normal used fairly mostly 1/1 sliders, 1/2 here and there with a consistent distance snap (ds.)
Whereas when you go to the Hard and look at the overall difficulty, it uses a fair bit of 1/4 and even at times it could use some 1/4 streams and a lot of 1/2.
This can be either so major that it would require another difficulty, or the Hard difficulty would need to be nerfed down to accommodate the spread.
Nerfing down a difficulty can be a fair option but it can also potentially lead to more issues such as if the Insane was also fairly dense and likewise with the Extra on the set, or another thing is that nerfing it down would simply require a complete remap. It all comes down to, it may just be easier to go through with making a new difficulty, even if it is the least favorable option to choose from.
Now when we think of comparing Hard between an Insane or Insane between an Extra, this is where things get a bit more complicated since now we have to consider the complexity and not just Rhythm density within a mapset.
The Overall Complexity
When thinking about the overall complexity, what does that mean? Well going off by just simply Rhythm Density/Spacing alone is not going to save your life and sometimes it can't be the only point you can have within spread especially regarding it around higher difficulties.
You have to consider things like the difficulty of the patterns, readability, etc.
An Insane can be more much dense than a hard but still can be fairly easy and reasonable for spread but an Insane that has lot of more complex patterns that would be more suitable for Extra combined with that makes a huge difference!
For example, At 180 bpm, an Insane on a set is using fairly simple 1/4 spacing that's stacked and uses fairly average 1/2 jumps with simple to read patterns that you can call it an overally straight forward difficulty.
But the Extra on the other hand, use a lot of 1/4 and sometimes adds more 1/4 jumps, doesn't stack as much as well as their 1/2 patterns can not only be much more jumpier, it can deal with a lot more reading challenges along with it when we considered things like Anti-jumps mixing in 1/4 and 1/2 in their patterns especially when it is mainly circles.
Such an Extra is so difficult in this case that a simple Insane difficulty that doesn't prepare you for anything that is listed and can come off as seriously problematic as essentially, the gap is wide enough to need another difficulty at the very least. Sometimes that may not be the case and it could use some fine nerfing but either way the spread is a problem to be recognized.
At the end there are other things that could be listed but generally this is the main 3 things to always look out for.