In Norðurland, the railroads have a large standard gauge, larger than the gauges of the most neighboring countries. However, in the border regions, many tracks have the same gauge as the neighbouring country. So I would tend to tag those tracks as railway = narrow_gauge - as the OSM wiki suggests (the most common gauge in a country should be dawn as standard railway (railway = rail).
However, the neigbour country would most likely tag that track as standard gauge - which would result in “magic narrow-gauge to standard-gauge transitions” at the borders, due to the style in which both types of rail are drawn.
So, what should I do in your opinion? Should I accept that “graphical glitch” or should I tag my narrow gauge railroads as standard gauge, even if they aren’t?