For example, C# and D#, in the diagram, are too close to each other. C# should be farther left, and D# should be farther right.
For instance if you learn that a harmonic minor scale is made of 1 2 3b 4 5 6b 7 you can find the notes of that scale in any key very quickly, for instance Bb harmonic minor would be Bb C Db Eb F Gb A
However this requires that you understand what are 1, 2, 3b 4, 4#, etc, and have enough practice in translating it to notes to do it quickly.
Also if you learn this, then finding the chords that can be derived from any scale becomes super easy.
Now I understand that this a hustle for many people because of the initial effort that requires before is actually usable, and it's more easy to use tools such as the one presented, I just wanted you to know that there is something better albeit harder.
I want to write my own and I struggle to find proper chords to melodic lines. Can anyone recommend resources to learn this (and tell me if harmonization is the proper term)?
[googles it] On the "minor scale" wiki page they mention those three scales - "In music theory, the term minor scale refers to three scale patterns". There is no one "minor scale", that I'm aware of. Well, maybe you were taught that way, I don't know. Dorian mode (i.e. white piano notes from D up to D) is another commonly used minor scale; there are others.
The site is remarkably comprehensive - circle of fifths and everything needed to both practice and understand the theory. Moreover, the site has a quirky design that's both cleaver and cute.