I suggest, that we should classify all overhead powerlines with at least one circuit with an operation voltage of more than 50000 volts as "high voltage line" and all other powerlines - except of overhead electrode lines of HVDC systems with an operation voltage of more than 50000 volts - as "low voltage lines".
This makes sense, as most official topographic maps do not show lines with voltages with less than 50000 volts.
Do not use the symbol "pylon" for "low voltage lines", use for this lines always "power pole". The reason therefore is, that at some zoom levels, pylons are displayed, but "low voltage lines" not and rows of pylons without interconnections look bad as they suggest a line under construction.

An electrode line of a HVDC system is a line used at a HVDC scheme with ground return for the interconnection of the inverter with the ground electrode. Such a line can be implemented as underground cable or as overhead line, whereby it can use the towers of the main DC line, separate towers or towers of AC-powerlines. As the conductor of an electrode line runs to a ground electrode, it has no high voltage against ground and can be implemented similiar to 10 kV AC-lines.
However as such a line is part of a transmission scheme using voltages of more than 50000 volts ( all HVDC schemes with overhead electrode lines are operated with such voltages) it should be always classified as "high voltage line", in order to show, that this is a line belonging to a line designed for more than 50000 volts.
One may ask: why are there electrode lines at all? Why is the scheme not grounded at the inverter?
The reason why a special electrode away from the inverter is used is the prevention of electrochemical corrosion, which would occur if the grounding would be done in an inpropriate manner.