The distinctive characteristic of French cathedrals, and those in Germany and Belgium that were strongly influenced by them, is their height and their impression of verticality. Each French cathedral tends to be stylistically unified in appearance when compared with an English cathedral where there is great diversity in almost every building. They are compact, with slight or no projection of the transepts and subsidiary chapels. The west fronts are highly consistent, having three portals surmounted by a rose window, and two large towers. Sometimes there are additional towers on the transept ends. The east end is polygonal with ambulatory and sometimes a chevette of radiating chapels. In the south of France, many of the major churches are without transepts and some are without aisles.

Answer this question, if possible (if impossible, reply "unanswerable"): What is the distinguiushing visual design feature of French cathedrals?
their impression of verticality