[gpsGuys]

Yes, Chicago is one of the toughest cities for GPS in the US.

Here's a peek into average building heights in downtown Chicago. Anywhere red, yellow, or orange we expect to have poor sky visibility. GLONASS being more popular has made Chicago slightly less challenging, before you could have trouble even seeing enough satellites to get a fix.

https://imgur.com/a/3bjiiRw

[wenc]

It gets even harder streets with like Lower Wacker Drive that are one deck below street level. There is almost no line of sight to any sats.