Below is a map of areas with the largest increase in Dem voter registration. I have provided more detailed demographic information of the two districts with the largest increase.
University CityThe racial makeup of University City is approximately 42% Black, 35% White, 18% Asian/Pacific Islander, 4% Hispanic, with the remainder not classified. (UC Report Card: Households, Age, Income, Race; p.7)
"The residents of University City can be described as young, highly educated, and diverse. Home to four universities and colleges, University City's student-aged population represents nearly half of the neighborhood’s total population. In addition, the area is becoming more ethnically diverse, with an estimated 7% increase in the minority population since 2000. The share of residents who have a bachelor's degree or higher is almost 40%, which is 20% higher than the city and 10% higher than the region." (UC Report Card: Households, Age, Income, Race; p.7)
West Philly"West Philadelphia is a vibrant, diverse, multi-cultural urban area, home to three excellent and world-renowned universities."
http://wikitravel.org/en/Philadelphia/West_PhillyConclusionThese two districts are highly educated and contain significant African American populations. In short, these are Obama's strongholds.