I suppose it also depends on how you define "space". Because there's not much to chart about space, per se. What you're really charting are star systems, and their positions in relation to other star systems. The bits in between is just vacuum. Literally. So the parts of the Alpha and Beta Quadrants that have been "observed" and/or "charted" are likely the sum of star systems, nebulae, spatial anomalies, etc. that have been catalogued, rather than an amorphous shape on a two dimensional "map".