Geometric sans serif typefaces – as their name suggests – are based on geometrical shapes, especially circles for their “o”. Many of these typefaces have their roots in the 1920s and 1930s, and often reflect the Art Deco aesthetic of that period.

Of the three sans serif categories, this is my least favourite for use on transit maps. Their rigid reliance on geometry makes them a little inflexible in use, and because many of the characters are so wide, the x-height is almost always small. This contributes to that Art Deco feel, but doesn’t help legibility very much. In general, the condensed versions of geometric sans typefaces don’t match their standard variants very well, as the “perfect circle” of the round letterforms has to be sacrificed in order to achieve condensation.  

Use of geometric sans serifs on transit maps include: Avant Garde Condensed on the Dallas DART map, Geometric 415 on the Maryland MTA map (actually works pretty well), Futura on Atlanta’s MARTA map, and Futura Condensed on this Freiburg im Breisgau map.

If you really need an Art Deco vibe to your map, then you could use a geometric sans, but I’d stay clear otherwise.

Next: Humanist sans serif – the big category!