This map (black, red, and blue inks) claims to be from 1917, but in red
depicts 1940s RRs. For subsequent discussion, I've highlighted certain of
those RRs with crossgatched lines. The previous tour page concentrated on
the mill area at lower right.
Oddly, this map depicts an unbuilt Pennsylvania Railroad (PRR) segment from
Dundalk east to Grays Yard (red overlaid with crosshatched purple). I speculate
the unbuilt route was proposed/surveyed prior to 1940, but remained unused
until the Baltimore Beltway followed it decades later.
Also depicted but never built is an east leg of the wye between the branch and
PRR main line at top. Only the leg leading to/from Bay View Yard at
upper left was ever built.
We'll follow the dark green hatched Gray's Spur line north from Grays Yard first,
then the dark red hatched Sparrows Point Branch.