The discovery of Norte Chico has also shifted the focus of research away from the highland areas of the Andes and lowlands adjacent to the mountains (where the Chavín, and later Inca, had their major centers) to the Peruvian littoral, or coastal regions. Norte Chico is located in a north-central area of the coast, approximately 150 to 200 km north of Lima, roughly bounded by the Lurín Valley on the south and the Casma Valley on the north. It comprises four coastal valleys: the Huaura, Supe, Pativilca, and Fortaleza; known sites are concentrated in the latter three, which share a common coastal plain. The three principal valleys cover only 1,800 km², and research has emphasized the density of the population centers.