Urban and Rural Population
The 2015 urban population is 14,839 or 25% of the total population while the rural population is 42,273 or 75% of the total population. Households distribution is 26% or 3,113 are in urban barangays and 74% or 8,865 are in rural barangays. The most populated barangay is the urban barangay of Bacolod with a population of 4,518. Among the contributory factors leading to the high population of Bacolod is its proximity to town center or the central business district (CBD), the high density of housing units and the presence of informal settlers in the river control dike and at riverbanks. The second most populous barangay is the rural barangay of Monbon with a population of 4,414. Monbon’s population growth is attributable to its location being alongside the national highway and relative proximity to town center, its vast coconut lands in moderately level slopes which are also used for residential purposes, and the presence of tourism establishments. Gabao, a rural barangay with a population of 4,286, is the third most populous barangay. Gabao is strategically located at the center of a catchment area covering the barangays of Bulawan, Tongdol, Gumapia and Gulang-gulang. The barangay is a nodal growth center in the area and with a growing commercial hub. The urban barangay of San Pedro is the fourth most populous barangay with 3,154 population. San Pedro is the largest in terms of land area among the urban barangays, contains part of the CBD, is traversed by the national highway and the site of major institutions. (Refer to Table DE-3)
There is a declining urbanization level, or growth in the proportion of population living in urban barangays, in the past 25 years. In 1980, 36% of the population are living in the urban area and the proportion dropped to 31% in 1990, to 27% in 2000, 26% in 2010, and to 25% in 2015. This declining trend is correlated to the disparity in the population growth rate of rural and urban barangays. The annual growth rate of urban barangays from 1995 to 2015 ranged from 0.34% to 1.15%, while the rural barangay’s growth rate ranged from 1.41% to 2.98% in the same period. The main factor contributory to this trend is the constraint on the availability of land for expansion of built-up areas in the urban barangays. The urban densities of San Julian, San Juan, San Agustin and Bacolod are at its highest. The expansion of built-up areas in San Pedro, which has a large land are, is constrained by the presence of irrigated rice lands. In comparison, 14 % of Sorsogon’s population lives in urban barangays in 2015. (Refer to Table DE-4)
Population Density and Built-Up Density
Irosin’s gross population density is 375 persons per square kilometer or 3.75 persons per hectare in 2015. Urban density is at 45 persons per hectare compared to rural density of 2.86. The highest population density is found in urban barangays of Bacolod with 246 persons per hectare, followed by San Juan at 205, San Agustin and San Julian at 140, and San Pedro at 12. The densest rural barangay is Gabao with 11 persons per hectare, followed by Gulang-gulang and Macawayan at 9. Rural barangays with lowest population density is Cawayan with less than one person per hectare, followed by Cogon, Liang, Mapaso and Tabon-tabon with only 1 person per hectare population. The population density of rural barangays is significantly lower since habitation areas are usually clustered on small areas surrounded by vast agricultural lands. Irosin’s gross population density is slightly higher compared to Sorsogon province’s 3.74 persons per hectare. (Refer to Table DE-5)
Hierarchy of Settlements
Barangay San Julian ranks first in the hierarchy of barangays as it is the seat of municipal government, the public market, the Catholic parish church, the public auditorium and majority of the commercial establishments of the CBD. While Bacolod maybe the most populous and densest barangay, it is considered as second in the hierarchy considering that the existing built-up use of the barangay is predominantly residential. Barangay San Juan and San Pedro are third in the hierarchy based on population density and significant presence of institutional and commercial establishments in the area. San Agustin is fourth in the hierarchy based on its population density.
Gabao is the fifth based on its population, population density and the built-up density. Gabao is the main nodal growth center in the west quadrant of the municipality and has the highest area of built-up land uses outside of the urban barangays. Monbon which is the most populous rural barangay ranks sixth in the hierarchy. Monbon is also a growth center for tourism and has significant built-up area. The barangay of Patag occupies the seventh rank in the hierarchy of settlements based on its population and its role as the nodal growth center in the eastern quadrant.