What does it take to photograph a shop in San Andreas? Specifically, where to do "refers to where to go, there are many mission locations"?

Sweet's mission (you can't open it until you finish Tenpenny's Burning Desire) is to buy guns in a gun shop south of Mad Dog Doc Villa, and then go to a park with a pond to grab territory. After completing this task, the site war and weapons store have been opened (the site war will be closed again in the second city SF).