Lines Tool

Lines versus Taxi-Lines

'Airport Line Markings' are intended for aircraft movement related things, like taxiway center/edge lines, runway hold markings etc. Just as Taxiways are for aircraft movement areas, only. They can have lights associated with them and they are written into the apt.dat.

'Lines' can look the exact same, have the same choices (plus many more if you use 3rd party addon libraries), but are closely related to polygons: Intended for everything else, they go just like polygons into the .dsf tiles. They can have lights, too, but these lights have to be placed as separate 'strings' then.

The three important things are

lines align exactly relative to polygons, as both are subject to the same compression when written to .dsf tiles. This is e.g. important when using a line to outline a polygon like the red/yellow./white striped 'safety area polygons'.
airport line markings will NOT exactly align with polygons. They also take up 5-7x as much space in scenery files and end up in a global database: ALL airport line markings at ALL airports globally have to be parsed by the simulator EVERY time X-plane starts. While .dsf tiles are only read if you fly near there. Reading binary .dsf content is about 5-10x faster in the sim as reading the text format apt.dat. So scenery complexity is WAY less of a problem, if that content ends up in .dsf tiles.
other users of gateway data like FlightGear and OpenStreetMap (yes - they do import our apt.dat's. Its part of why ESRI gives WED free access to their imagery ...) do read the apt.dat, only. So lines important to taxiway structures should be in the apt.dat. OSM and FG both have their own roads/art objects etc. The OSM guys even asked to have the road markings removed from the apt.dat, so they don't have to filter out those lines: They can't tell a yellow dashed taxiway line from a yellow dashed road center.

That is why I strongly recommend to draw items that normally do not require lights AND are not important to the movement of aircraft as lines and not as airport line markings. Its almost an 'yellow' vs 'all other colors' thing. For example

Apt Line Markings: * taxiway center, edges - in particular if they go along with lights * taxiway hatches (wide yellow 'don't taxi here' side bars) * runway holds, other holds

Lines: * outlines around polygons * outlines around ground painted signs * aircraft ramp parking markings * ground traffic only relevant markings on the apron * road markings * anything outside the airport boundary * anything not on or near a taxi or runway

Airport Line Markings can be converted into Lines and vice versa with Edit -> Convert To in WED 1.7 and newer. Actually - WED shows the real color of a 'Line' in the pictorial (zoomed out) preview - while all non-yellow 'Airport Line Markings' are always shown as white, only.

Starting with WED 2.2 the 'Convert to' will automatically set matching 'Resource' or 'Marking' properties when converting either way. And allow to use the GUI for selecting Apt Line Marking styles on Lines as well.