"What does the national line (purple bar) represent in the interactive chart report?"
The purple line shows the national median for that measure. The shaded purple area above and below the line represents the distribution of schools above and below the national median. The area above the line represents how tightly the closest 25% of schools fall above the median and the area below represents the 25% closest who fall below. Therefore, the purple area is an indicator of not just the national median value, but how closely the national population tends to conform to that median.
"Why aren't there any national norms or comparison lines in my charts?"
Some of the measures are newly introduced and the responses collected are still under analysis. Therefore, some of the measures do not have national comparison lines. Once we are able to collect enough statistically representative data those lines will appear in your reports.