Questions on VFR sectionals and TACs

Bob Noel writes:

In article ,
Christopher Brian Colohan wrote:

North of Boston you will find a large white-ground circle outlined by
a thick cyan dashed line.

Not anymore (look at the 74th edition of the NY sectional)

Heh. Don't have that one yet. :-)

The meaning of white ground or a thick cyan dashed line is not defined
in the chart legend, nor is it defined in the book you point at. Any
guess what this is? (And why the FAA thinks it is worth putting on
the chart, but not worth documenting what it means?)

On the 73rd edition of the NY sectional there is indeed a note
that P-67 is expanded by special notam.

I found the note, but only figured out what it was associated with
_after_ someone explained the dashed circle to me. I guess I find it
puzzling that there are symbols used on the map which don't appear in
any legend... (Especially when just adding them to the legend with a
description like "heavy cyan dashed line == TFR outline" would clear
everything up.)

Chris