Original: The first six seasons of the show were all based in Los Angeles and nearby locations—both real and fictional—in California, although occasionally other locations have been featured as well—most notably, Washington, D.C., where a portion of the episodes took place during the fourth and sixth seasons.
Simplified: The first six seasons of the show were all based in Los Angeles and nearby locations  — both real and fictional  — in California, although sometimes other locations have been used as well.