AerospaceGuy said:
ahhh so to use the top post as an example while i'm playing C:

ctave::5th i'm in the key of C
and if I were to play say A:

ctave::3rd I'd be in the key of A. So you can be in the "key of C" all over the fingerboard just as long as you're bassline is based on a C scale.
If you're talking about playing over changes, arpeggios (chord tones) are a good place to start. When doing this, it's always about the chord of the moment, at least at first. For example, outlining a C major chord you use the root, third, and fifth. The root is C (of course), the 3rd is the third note of the C scale (E) and the fifth is the fifth note of that scale (G). The triad (three notes) are the basic building blocks of the chord. C minor would be root, minor 3rd (or flatted 3rd) and 5th, so that is C, Eb, and G.
Now let's take a commong chord progression: C, A min, F, G. Note something interesting. Let's say we're in the key of C. C is the I chord because it's built on the first note of the C major scale. A min is the vi chord (note that it's lower-case, cause it's minor), as it's based on the 6th note of the C major scale. F is the IV chord, and G is the V chord.
Now, as you figure out these triads, note something else. C (C, E, G); A minor (A, C, E); F (F, A, C); and G (G B D) are ALL notes in the C major scale, because those chords are diatonic to the key. When you use a major scale as your key, you get the following chord types:
I: major
ii: minor
iii: minor
IV: major
V: major
vi: minor
vii: minor b5
So in the key of C, the diatonic chords are:
C major
D minor
E minor
F major
G major
A minor
B minor b5
I'm not going to get into sevenths here, but just start seeing how this all fits together.