This is a very intuitive way to understand the connection of chords within one scale if you want so.

So for C you have these 3 couples: C a, F d and G e

The idea is to get from one point to the other without thinking, but instead through visual patterns and intuition.

So lets take a basic triad of C to start from: d:10 g:9 b:8

First lets try to get from C to a. You could think of the tones ceg (C) and ace (a) but you could also realise that one tone changes plus 2 (it’s bit of a math thing at first)

So that’s all you need to know is that one of these tones goes plus 2.

And it is g to a. So just by knowing that, when you hold down this triad shape, just try moving any of the 3 tones plus 2 and you will notice that 2 of these make a pretty weird shape already and therefore it comes very intuitive which one to use. But if that’s not weird enough already you could make it sound simply and surely it’s not how a minor relative would sound. You don’t need to know though where is the g, it’s purely visual and auditory thing.

Once you found the shape it is pretty distinct triangle, easy to remember.

Now lets go from a to F. Here one tone changes plus 1. ace ac+1f.

You might already remember this shape anyway from the F barre in the Ashape.

So again try moving any of these tones plus one and find out yourself.

From F to G you just move all plus 2.

From F to d you go minus 2 for one tone, same from G to e.

When you go back to C triad you could also move to e from there.

ceg egb…you see the c moves minus 1, so one tone minus one

You also could go from C to a G to the left. And this time when you try there is another major chord that could come up, that doesn’t though fit in.

From C to G it is ceg gbd ..one tone goes minus 1 and another minus 2. This one is a bit more fun to try to find.

So after a bit exploring you’ll intuitively get a hang of what tones move.

If you are at G to the right, if you want a G7 just move one tone minus 2, it’s also a distinct triangle. Btw when you are in this Ashape triad, just as with the E- and D shape triads, the basic tone is always in the middle.and the 5 is always above, so therefore the 3rd is the lowest tone and it’s easy to go to a 4 chord or add9/ sus2 from the third. Just like you can easily make a major 7 inbetween the 1 and the b7 or minus 1 simply from the 1.

When you approach it this way you will remember it better if you even need to cause you could just use your ears, as opposed to learning it without exploring.