Originally Posted by: axemaster911My key selections are dictated by open string notes. I find it very useful to choose a key that has all, or most of the open string notes in that key. It gives great sound dynamics, and ease of play, even when moving down to higher pitches. Key selection may also be dictated by the vocal range of the singer, but do I understand why one key is dominant over another, no. I am not even sure what you mean by dominant.
These principles you are trying to explain will be best grasped by those of use that are curious if you can find a way to show them in relation to the fretboard, and appeal to a wide range of skill levels. For that you effort im sure would be greatly appreciated. :cool:

The post by CSchlegel is excellent!!! I encourage you to study it over and over and it will really help to grasp Key signatures and the relationship of chord structures. Once you're comfortable with the logic, apply the same pattern to the G MAjor scale ( notice that G is the fifth note in the C MAjor scale, so G is the dominant of C). The dominant note (fifth) will share 6 of the 7 notes from the root scale when the same intervals are used starting with the dominant note in the root position.
Example: C Major= C-D-E-F-G-A-B. G Major= G-A-B-C-D-E-F#.
The only difference Between C MAjor and G Major is F#.
Now let's take the intervals to create a G7 chord (aka dominant 7th chord)
1 (root)-3-5-7b. the 7b changes F# to F so the notes are G-B-D-F which makes a perfect fit with C where GMaj7 would not because it uses F# in it's chord structure.