We used the HI data from the LAB survey to map the ring-shaped gap in HI density which lies slightly outside the solar circle .
Adopting R _ { 0 } = 7.5 kpc , we find and average radius of 8.3 kpc and an average gap width of 0.8 kpc .
The characteristics of the HI gap correspond closely to the expected ones , as predicted by theory and by numerical simulations of the gas flow near the corotation resonance .