While I don't know so much about geography specifically shaping music , there is research about it shaping language (for example the affect of geographic isolation on accents and dialects). There is, in turn, lot of material on our language shaping music. That is definitely worth looking into. There are also obvious examples of subject matter like mountains, deserts, or the sea, that would be less likely to come from regions distant frome those. Another element of 'landscape' to consider is the weather and seasons. My area never gets any snow, only has a few nights below freezing, and experiences a great die off of plants in the Summer. Thus, I would think it unlikely there are many Ohlone folk songs about winter bringing snow and severe fasting.

If you extend the notion of 'landscape' to include the environment, flora, fauna, and agriculture, the effect is undeniable. Harvest songs, songs personifying and moralizing various crops/trees/flowers, hunting songs, etc. There are also instruments and tunes that mimic the sound of an area's birdcalls or the noises of their animals. The name of a specific song escapes me at the moment, but there are some banging tunes for the erhu that mimic horse sounds. A lyrical example could the preoccupation with hops shown by some Kentish folk music.

As Manitas said above, many now live in cities. However, I think man-made landscapes have just as large an influence as natural ones. Mines, factories, and trains all have their own repertoire of folk songs. I don't see why 'urban' as a landscape shouldn't be counted. Where there are folk, there is folk, after all.