I am in the process of fleshing out a couple of the ideas I had for campaigns and remember coming across a chart people used for mapping story arcs, but cannot find it now. From what I remember it looked like a 3x5 grid, each column being a different story arc, and each row being a stage of the arc or something along those lines. Does that ring a bell to anyone?

Also what is your go to method or resource you use for mapping out your story arcs for your campaigns? Currently I'm using Mindly on mobile, it's simple and is aesthetically pleasing IMO.

I'm old-fashioned.  I write on a yellow legal pad.  I usually start with a word cloud.  Sometimes I have imaginary conversations with NPCs to figure out what they want.  Right now I have about 5 ideas I want to stitch together into an all-dwarven campaign.  When I get them in the right shape and the right order, they'll have a nice natural flow to them. 

for my latest campaign the main story arc foe levels 1-6 fell out almost naturally from the world I had created. I am now working out the details with pos it notes on a board. I run a Kanban board so ideas on one side and then as I work on them to flesh them out they develop into encounters or parts of my world. I generally focus on the ones that are most immediate to why my party are doing and things will come off and get added to the backlog of things not yet fleshed out all the time. 

I like to plan mine around character level, and set up a chart similar to what the OP suggested. Down the side I’ll have planned events/plot lines. Across the top is levels. Then in the boxes, I’ll write what would happen with those events and plots at those points, if the PCs don’t intervene. Then when the characters do something, I adjust what’s in the boxes as necessary. Sometimes big changes, sometimes small, sometimes none, all depends on what the characters do. I like to think it strikes a balance between PCs actions mattering, and the world moving forward on its own. 

I usually base it around tiers of play, though not always precisely. I usually have a set idea of the events that will take the players from levels 1-5 (I use milestone) at the start of the campaign. By the time they get to level 5, I should have a vague idea of what will happen in levels 6-11, and a good idea of what will happen to take them to level 6 (though only an outline, I try not to railroad my players).

I don't really plan story arcs per se. The players make the story happen.

I have stuff going on in the world. If the players interfere, things change. If not, they keep chugging along. I guess the "things going on in the world" could be a long story arc, if the players don't find a way to interrupt it.