In AMWOL, a "line of contact" and a "chain of contact" are
slightly different things. A line of contact exists between two
units, two cities, or a unit and a city. Lines of contact are
defined in GITM rule 10.2. Chains of contact are composed of a
series of lines of contact. A unit has an unbroken chain of
contact to a target city if it is in that city, or if it has a
line of contact to a CQ not longer than 2 squares which has a line
of contact to the city not longer than 8 squares, or if it is in a
different city (or has a line of contact to a CQ which has a line
of contact to a different city) which has lines of contact to the
target city, or to a sequence of friendly-controlled cities, all
with lines of contact between consecutive members of the sequence
and each line not longer than 10 squares, ending at the target
city. For some purposes (drawing reinforcements and moving on
peace/truce turns) consecutive members can be two unblockaded
ports as well as having a line of contact between them.
Example (from NWOL): Naples is at war with France. Cosenza is
controlled by France. Reggio is blockaded by French ships but no
other Neapolitan port is. NE1IN is in Taranto at I3-S7 and NE1CQ
is at I2-S6. Then NE1IN has a chain of contact to Taranto since it
is located there. It also has a chain of contact to Bari at I0-X5
because it has a line of contact to NE1CQ at I2-S6 (1 square long)
which has a line of contact to Bari (2 squares long). It also has
lines of contact to Aquila, Gaeta, and Napoli via Bari. For some
purposes, it also has a chain of contact to Palermo and Siracusa
because it has a line of contact to Bari and Bari, Palermo, and
Siracusa are all unblockaded ports. It does not have a chain of
contact to Cosenza because that city is French-controlled, and it
does not have a chain of contact to Reggio because there is no
sequence of friendly cities, all with lines of contact of 10
squares or less, leading to Reggio (Cosenza is not friendly,
Napoli and Bari are both 11 squares from Reggio, and Reggio is
blockaded so the chain of contact cannot be drawn by sea). If
Cosenza was not blockaded, NE1IN would have a chain of contact to
it. If Cosenza was not French-controlled, NE1IN would have a line
of contact to it and then through it to Reggio.