An analysis of population by zipcode was conducted to compare regional demographic characteristics with college credit enrollment for the three colleges in the San Diego Community College District, and to determine college participation rates for the adult population in the district. Enrollment data for the fall 1991 semester were compared with population data from the 1990 census. Study findings included the following: (1) the total student population at San Diego City College (SDCC), regardless of place of residence, is 40.9% White, 20.7% African American, 19.9% Latino, 5.4% Asian, 4.3% Filipino, 2.2% Southeast Asian, and 0.3% Pacific Islander; (2) the adult population of the SDCC service area is 14.3% African American, 22.6% Latino, and 9.6% Asian, Pacific Islander, or Filipino; (3) enrollment from the service area of 24.9% African American, 19.6% Latino and 8.7% Asian, Pacific Islander, or Filipino; (4) participation rates from the SDCC service area are 4.42% for African Americans, 2.2% for Latinos, and 3.35% for Asians, Pacific Islanders, or Filipinos; (5) enrollments at Mesa College and Miramar are 64.3% and 63.6% White, respectively; and (6) less than 35% of students at Miramar College live within the service area. Includes tables and maps showing adult population by race and zipcode; enrollment figures by race for each college in the SDCCD; and information on service area demographics, enrollment by race, and participation rate by race for each college in the district. (KP)