San Fierro has a low population as it doesn't really contain major CnR activities. I am willing to fill it with civilians as clearly that's the real purpose of that city. One method is to add as much civilian activities as possible there so the people can pretty much do anything without leaving the city.
By adding a Waste drop point
here, people could work in the city itself thus we could increase its population. It doesn't harm anybody so I don't see why could this be a bad idea.
Coordinates for the Waste drop pointX: -1840.8157 Y: 116.1058 Z: 15.1172Regards!