This question already has an answer here:
My client wants a map of bus routes rendered as white lines with blue casing. I'm using QGIS 2.8.2 on Mac OSX 10.10.5. I found a .kml dataset here: http://developer.trimet.org/gis/data/tm_routes.kml. I also tried using the .shp.
When I add the layer to the map and apply a cased line styling, some of the routes render as nice unified lines and others render as segmented, like earthworms:
I could easily cheat and render a duplicate layer (featuring only the thin white lines) on top of this one.
Why do the lines render in different ways?
Is there a way to render them all as unified?