Tritipeskul pulled datat from the Census Bureau's Local Employment Dynamics database:
"Many big job centers (...) are served by transit. These job centers include Warner Center in Woodland Hills (Orange Line BRT); Pasadena (Gold Line); Santa Clarita, Palmdale and Lancaster (Metrolink); Long Beach (Blue Line); and downtown Los Angeles.
Others are not at the moment. For example, the northwest San Fernando Valley is a darker shade of blue. It will soon have the Orange Line busway extension, scheduled to open in 2012 and a project funded by the Measure R sales tax increase approved by L.A. County voters in 2008."
Excellent maps are available at The Source.