The latest voter registration report, released by the secretary of state on Friday, shows that the surge in Democratic registration continues in Ventura County. There are now 4,123 more Democrats than Republicans on the county's voter roll -- a dramatic shift, given that when registration closed for the Feb. 5 presidential primary Republicans still held a slim advantage.

I was curious whether this political shift was concentrated in any specific areas in the county or whether it was an across-the-board phenomenon, so I checked the city-by-city reports from four years ago and compared them to where things stand today.

The data show that Democrats have made gains in each of the county's 10 cities, but that the biggest shifts have come in western Ventura County. The largest gains have come in Ojai (8.9 point increase), Port Hueneme (8.2 points), Ventura (7.4 points) and Oxnard (7.2 points).

Arguably the biggest shift has been in Ventura, which four years ago was a city that was essentially split down the middle politically -- 40.1 percent Democratic, 39.3 percent Republican. Ventura has now become a solid blue city, with 42.8 percent of its voters Democrats and 34.6 percent Republicans.

The shifts in eastern Ventura County have been in the same direction but slightly less dramatic. The Republican edge in Thousand Oaks has dropped by 5.7 percentage points, from an an 18.1 point advantage in 2004 to a 12.4 point edge today. In Moorpark, the GOP edge has diminished by 5.4 percentage points, in Camarillo by 4.9 points and in Simi Valley by 3.4 points.

Two things haven't changed: The most Democratic city in the county remains Santa Paula (30.6-point Democratic edge) and the most Republican city remains Simi Valley (15.2-point GOP advantage).