Parts of Bohol, Cebu, Samar and Palawan sit on limestone, which dissolves. Here is why that matters for a property and what to look for, since no national layer rates it.
Some Philippine ground is built of limestone. Bohol is the famous example, with the Chocolate Hills, but limestone also underlies parts of Cebu, Samar, Palawan, Bicol, and elsewhere.
Limestone has a property that other rock does not: it dissolves slowly in slightly acidic water, which is what rainwater is. Over a long time that creates caves, underground channels, and voids. This is called karst.
Karst ground is usually stable. When it is not, it fails suddenly.
Rainwater seeps into limestone and dissolves it along cracks. Over centuries this opens passages and chambers. The soil above bridges over them, held up by nothing much.
A sinkhole forms when that roof gives way. Triggers include heavy rain, a change in groundwater level from pumping, vibration, or the extra load of a new structure.
The distinguishing feature is that there is often no warning. Slope failure usually gives signs. A collapse into a void may give a few small cracks and then go.
A hazard screening reads national datasets that model flood, landslide, storm surge, faults, terrain, and volcanic proximity. There is no equivalent national point-level sinkhole susceptibility dataset for the Philippines of the kind that would let a screening report a rating honestly.
We would rather say that plainly than invent a number. The same principle governs how we label liquefaction as an estimate rather than a measurement; see what liquefaction is, and why we label it an estimate.
The Mines and Geosciences Bureau produces geohazard assessments that in some areas cover karst and sinkhole concerns. That is the office to ask.
You are in limestone country if you see:
Local names help. Toponyms referring to caves, holes, or springs are a clue that people noticed something a long time ago.
The answer is not a hazard app. It is a geotechnical investigation, and in karst areas that investigation needs to be designed for karst, which usually means more boreholes and sometimes geophysical survey rather than a single test pit.
Ask the MGB regional office whether the area has a known karst or sinkhole concern. Ask the municipal engineering office whether there have been incidents. Ask the neighbours, who will remember.
This is the clearest case in the whole hazard set where the screening tells you what it does not cover. A CheckHazard report has no sinkhole layer, and a clean report in limestone country says nothing about voids underground. That question belongs to the MGB and to a licensed geotechnical engineer, and in karst areas it is worth the money.
CheckHazard does not replace a professional geotechnical or engineering survey.