Hi !
I agree with the "quick glance" approach.
French VFR enroute charts, both from IGN/SIA and Cartabossy, provide a quick way to figure this :
- IGN/SIA : airfield icon depicts whether the longest runway is above or below 1000m. Less : blue outline, no runway symbol ; More : blue disk, cut out with a transparent shape showing what the main runway orientation is.
And 3 numbers are displayed below the airfield identification : elevation, frequency, runway length in hectometers (length = 1100m, figure shows 11)
- Cartabossy : airfield symbol changes when runway is less than 400m, between 400 and 1000m, and above 1000m (3 symbols).
Since there already are examples of "how to quickly know that in one glance", I think that concurs with the UX approach described by Marc.