The figure was based on the actual tax mapping conducted by the said office. The same figure was also used in the old town plan of Quezon and was validated by using a digital planimeter. With this figure, Quezon is the 13th largest of the 34 municipalities of Isabela and the 3rd largest out of the 11 municipalities of District 2 (San Mariano being the largest at 1,469.50 km², followed by Aurora at 300.56 km²). It is larger than its neighbors Mallig (133.4 km²) and Roxas (184.8 km²). Quezon is politically subdivided into 15 barangays. Poblacion Centro (Settlement 1) consists of Alunan (Southeast Poblacion), Arellano (Northwest Poblacion), Santos (Northeast Poblacion), and Samonte (Southwest Poblacion). The rest of the barangays are rural barangays. The municipal landscape of Quezon is characterized by a mixture of relatively flatlands punctuated at certain points by undulating and rolling terrain, with mountain ranges flanking its eastern and western sides. The low-lying hills ad surrounding mountains ranges are slightly dissected by intermittent creeks and waterways, which act as natural drainage avenues of accumulated run off water coming from the uplands. The physiography of the municipality falls into two basic categories: an alluvial plain and a mountainous terrain. The central plain, where the Poblacion is located, has an elevation of about 100 meters above mean sea level, and is predominantly characterized by low relief and moderately sloping areas. Three fourths of the town is covered by these flatland which may be considered as a broad alluvial plain with recent depositions and residual soils. These areas are found sandwiched between the eastern and western uplands as well as on the other side of the Sierra Madre foothills. The south-western portion is characterized by the low-lying hills with undulating and rolling terrain, having elevations ranging from 90–120 meters above mean sea level. These are basically shale and sandstone materials which dominate the Isabela-Kalinga boundary. The eastern edge, meanwhile forms part of the foothills of the major mountain range in the area and dominates the eastern flank of Quezon. This high relief area has peak elevations of up to 200 meters above mean sea level and is composed primarily of volcanic rocks. Pedologic surveys conducted by the Bureau of Soils Management of the Philippine Department of Agriculture have identified two major soil series or categories in Quezon.