TomTom maps and their file sizes

I have to TomTom map sets, of the US and Canada, and the other is Western Europe. The Western Europe map barely fits on a 1 Gb card, but the US and Canada map easily fits on there. Are there that many more roads in Western Europe than in the whole US and Canada together??

The European roads are just made from denser asphalt.

The reason is probably that in the US road systems tend to be grid-like, whereas in Europe they are not much structured. If one encodes this information in a vector format, then grid-like roads use up much less information.

Also: Kansas.

(if you're from Kansas, then I meant to say "Also: Nebraska")

Another possible reason is that the European maps are more recent and contain more data (elevation gain, cycle lanes, traffic restrictions for certain vehicle types...).

another factor will be that the road network in Europe is much, much denser that in north America.