The gap of the contamination level was clearly shown in this experiment done in Tokyo and Okinawa, on 12/29/2011.
In Tokyo, they measured radiation in Yoyogi Shibuya.
In Okinawa, they measured radiation in Naha shintoshin park.
Tokyo (Street, not gutter)
2cm from the ground : 0.611 microSv/h (493 CPM) (The total of α,β,γ)
On the ground : 0.107 microSv/h (156 CPM) (Only γ)
Okinawa (Street, not gutter)
2cm from the ground : 0.110~0.145 microSv/h (135 CPM) (The total of α,β,γ)
On the ground : 0.046~0.056 microSv/h (91 CPM) (Only γ)
(Source)
Iori Mochizuki