The images below have been adjusted to the same scale. One is an image of Northern Japan, and the other shows the size of the area affected by radiation from Chernobyl. The arrow indicates the location of the nuclear plant.
This only relates to long term health impacts. At Chernobyl, only workers at the site were affected by radiation sickness. The images show how bad a Chernobyl style release could be for the Japanese.
(Images from wikimaps and wikipedia)
The precise patterns of fallout would depend on wind directions and rain fall. Tokyo is the world's largest metropolitan area, with 35 million people.
Fortunately, the latest news from Japan is good. Major progress has been made in adding water to spent fuel ponds and restoring cooling. However, there is much still to be done.