I live in Canterbury, England. It's got a big population, so loads of Pokemon; beautiful river walks and loads of parks thanks to its strong conservation focus, so loads of great places to walk; and an immense amount of history thanks to its big roles in both Roman and Norman conquests, so loads of Pokestops and Gyms. It should be an amazing place to play this game! But...
Thanks to Canterbury Council's refusal to allow developments taller than the ancient city walls, there are no phone masts allowed in the city. Which means 3G/4G coverage is abysmal inside the city. So I have this walk along the outskirts, along a river, where I can pick up Pokestops along the route but as soon as I cross the river to the other side my 4G reception just drops off a cliff. Unless you can connect to shop and cafe WiFi inside town, there's nothing you can do to play this game =(
So distressing when you can see SOOOO much inside! Reception comparison on each side of the river: