Iloilo City is an alluvial plain which mainly consists of river and coastal deposits of Holocene. Considering the layers confirmed by the soil profile and sedimentary environment, the area is classified as two (2) sedimentary basins; one is the Jaro sedimentary basin and the other is the Iloilo sedimentary basin.
Characteristic of an alluvial plain and like most other coastal cities in the country, Iloilo City is relatively flat and is made up largely of a slope less than 3 degrees covering an area of 6,570.15 hectares or more than 83% of its total land area. Only 2.26% of the city’s land area is with an elevation of more than 8%. The entire city is suitable for urban use and is presently built up with widely distributed residential, commercial, institutional and industrial buildings. 83.87% of the city’s area is within the slope category of less than 3% whereas the 5.23% area is within the 3-8% category and the 2.26% area is greater than 8% slope category. The suitability is of urban use all throughout the areas of Iloilo City.