◢ Research & methodology
Every CheckHazard report is built from publicly available datasets published by Philippine government and academic institutions. No proprietary models, no internal scoring, nothing reverse-engineered from third-party data resellers. This page walks through the seven institutional sources we read from, and the documented methods we use to turn each source into the findings you see in a report.
◢ I · Source datasets
What each source publishes, what we pull from it, and which sections of the report depend on it.
01 / 07
What they publish
Modeled flood zones at 5-, 25-, and 100-year return periods; landslide susceptibility polygons; storm surge zones at SSA levels 1 through 4.
How CheckHazard uses it
Three of the five Top Concerns on every report — Flood, Landslide, and Storm-surge — are driven directly off NOAH's polygons. We check whether the geocoded property sits inside the polygon, and if not, how far away it is. The polygon's level (1=Low, 2=Moderate, 3=High) becomes the finding's severity.
02 / 07
What they publish
Funds and supervises the UP NOAH Center, the Philippine Institute of Volcanology and Seismology (PHIVOLCS), and several other research arms whose datasets we use.
How CheckHazard uses it
DOST itself doesn't ship a hazard polygon — it underwrites the agencies that do. We cite DOST on every report so readers can see where the upstream research dollars come from.
03 / 07
What they publish
Mapped traces of active fault lines across the Philippines, plus the official inventory of active volcanoes.
How CheckHazard uses it
We measure the straight-line distance from the property to the nearest fault and the nearest active volcano. Distance bands then drive the Fault and Volcano findings, and the Legal Constraints section flags any property within the 5-meter NSCP no-build buffer or the 500-meter PHIVOLCS advisory band.
04 / 07
What they publish
An openly licensed global compilation of active fault traces, with metadata harmonized across countries.
How CheckHazard uses it
Used as a cross-reference layer alongside PHIVOLCS. Where the two datasets disagree, we surface the more conservative reading so a buyer never misses a fault line a permit reviewer would catch.
05 / 07
What they publish
Geohazard susceptibility maps — landslide, debris flow, and alluvial fan zones — published nationwide.
How CheckHazard uses it
Debris-flow and alluvial-fan findings are point-in-polygon: either the property sits inside an MGB-mapped zone or it doesn't. The landslide layer is also cross-checked against NOAH's landslide susceptibility for stability.
06 / 07
What they publish
Authoritative administrative boundaries — 1,642 municipalities and 42,048 barangays — and Philippine base maps used by every government agency.
How CheckHazard uses it
When the report says "Quezon City · Project 4" or "Tagaytay · Maitim 2nd West," that locality string comes from NAMRIA. Boundaries are also used to confirm a property falls inside Philippine territory before any hazard lookup runs.
07 / 07
What they publish
Named rivers, creeks, and esteros across the Philippines, plus the streetmap basemap layer used in the report's interactive map.
How CheckHazard uses it
We measure the distance from the property to the nearest named waterway. That distance drives the Waterway finding (a 3-meter Water-Code easement applies for creeks; 20 meters for rivers; 40 meters along coastlines), which the Legal Constraints section reads when computing buildability.
◢ II · The pipeline
The same machine-readable transform runs for every Philippine property. Same datasets, same thresholds, same output shape — the only thing that changes between two addresses is the data the pipeline reads.
Step 01 · Geocode
Google Places turns a typed address into a precise latitude and longitude (typical accuracy: 10 to 50 meters from the actual lot). NAMRIA boundaries confirm the point sits inside Philippine territory before anything else runs.
Step 02 · Spatial query
A single PostGIS query asks every authoritative dataset the same question: "Is this point inside your polygon? If not, how far is the nearest edge?" Five hazard tables — flood, landslide, storm surge, debris flow, alluvial fan — plus active faults, named waterways, and active volcanoes all answer in milliseconds.
Step 03 · Raster sample
From the SRTM elevation raster we read the property's exact elevation in meters and ground slope in degrees. Two small numbers — but they feed the Site Characteristics table, the Liquefaction screening estimate, and the Historical Event comparison.
Step 04 · Apply thresholds
Raw distances and polygon hits become severity ratings using documented thresholds — a property within 100 meters of an active fault is Severe; 100 to 500 meters is High; 500 to 2,000 meters is Moderate. The same banding pattern applies to every hazard, and every threshold is shipped on the report itself in the Rating Guide.
Step 05 · Assemble
The findings flow into a structured report. Section I picks the overall rating from the worst non-estimated finding, Section III lists every finding in priority order, the Map Reading Guide explains the polygons drawn, and the Insurance Guidance section translates each severity into a premium band.
◢ III · The eleven methods
No proprietary scoring, no internal weights. Every threshold, distance band, and proximity buffer is published — including the ones you'd argue with.
“Is the property inside a hazard zone?”
PostGIS draws an imaginary horizontal line from the property and counts how many times that line crosses the polygon's edge. An odd number means the point is inside. Done for every flood, landslide, storm-surge, debris-flow, and alluvial-fan polygon in the database.
“How far from the closest hazard zone?”
When the property isn't inside any polygon, we measure the straight-line distance in meters to the nearest edge. The map's spatial index narrows the search to nearby candidates so this stays fast even with millions of polygons in the dataset.
“What's the elevation and slope here?”
Elevation is sampled from the SRTM raster — a grid of altitude readings spaced 30 meters apart across the Philippines. The slope between adjacent grid cells gives the ground gradient at the property.
“Is 466 meters from a fault Moderate or High?”
Distances and polygon levels turn into severity ratings using documented bands. Active faults: under 100 m is Severe, under 500 m is High, under 2 km is Moderate, beyond is Low. Every hazard has a similar table, all shipped in the report's Rating Guide.
“Just outside a hazard zone still counts.”
Geocoded coordinates can drift up to 50 meters from the actual lot. So a property reading as 30 meters outside a flood zone is reclassified as inside it — better to surface the question than miss it. The buffer is named in every report's methodology.
“Being near a High zone is still concerning.”
A High-severity polygon next door affects the property even if it doesn't physically touch. Up to 200 meters from a Level-3 polygon, we surface the proximity in the finding so reviewers can see why an LGU might require additional setbacks.
“Soft soil multiplied by shaking risk.”
PHIVOLCS' liquefaction map isn't open data, so we screen the property using signals we already have — low elevation, flat slope, proximity to a waterway (soft-soil indicators), and proximity to an active fault (shaking indicator). The result is labeled Estimated and never sets the overall report rating.
“What's the cost-of-cover signal?”
Each hazard severity translates to one of three premium bands — none, elevated, or prohibitive — across three independent policies (flood/surge, earthquake, volcanic). Not a peso quote, but a budgeting signal: this property will price as standard, expect riders, or face declines.
“Is this property legally buildable?”
Two laws are checked automatically: the NSCP 2019 fault-trace rule (no permanent structures within 5 meters of an active fault) and Philippine Water Code Article 51 easements (3 m for creeks, 20 m for rivers, 40 m along coastlines). Properties inside either zone are flagged as no-build under PH law — not a risk surcharge but a permit blocker.
“Did Ondoy put water above this property?”
Documented Philippine disasters (Ondoy 2009, Yolanda 2013, Ulysses 2020, Kristine 2024) come with measured inundation depths or shaking intensities. We compare each property's elevation against those recorded values and report the exceedance: Ondoy peaked 0.6 meters above your floor here.
“What are the three worst findings?”
Findings are ranked by measured severity, with three slots reserved for Flood, Landslide, and Storm-surge so the headline trio stays consistent across reports. The single overall rating is the worst non-estimated finding — never set by a screening estimate like liquefaction.
◢ IV · The composite rating
One rule, one outcome. The composite is never set by a screening estimate.
Pin the Top Concerns trio first
Flood, Landslide, and Storm-surge always occupy the first three slots — the hazards Filipino property buyers ask about most. They appear regardless of measured severity, so a Low flood reading still gets cited as a Low flood reading.
Rank everything else by severity
Fault, Volcano, Debris-flow, Alluvial-fan, Liquefaction, and Waterway findings are sorted from worst to least, with the worst measured value floating to the top. The ranking is purely numerical — no editorial overlay.
Set the overall to the worst non-estimated finding
Liquefaction is currently the only screening estimate, and it never sets the headline. A property whose worst measured hazard is a High landslide reading lands at Severe, not at whatever the liquefaction screen says.
Name the driver in plain English
The report names which specific finding set the rating, so a Severe report driven by a 90-meter fault distance reads differently than a Severe report driven by a Level-3 flood polygon. Same severity number, different next steps.
◢ V · What CheckHazard does not claim
The honest limits of the inputs we work with.
Geocoding precision is finite.
Google Places resolves Philippine addresses to within roughly 10 to 50 meters — the limit of street-centerline data. We add a 50-meter buffer to absorb that drift, but a property right on a hazard polygon edge can still read as edge-of-zone rather than fully inside.
Source datasets have publishing cycles.
NOAH, PHIVOLCS, and NAMRIA update on their own schedules. CheckHazard reloads each layer when the issuing agency publishes a new release — between releases, our reports reflect the latest snapshot, not real-time conditions.
Liquefaction is a screening estimate.
PHIVOLCS' authoritative liquefaction map is not openly licensed. Our screening estimate uses signals we already have (low elevation, flat slope, soft-soil indicators) and is labeled as such — never authoritative, never the rating driver.
Tawi-Tawi 100-year flood has no source layer.
The NOAH dataset for Tawi-Tawi 100-year flood is empty at the source. Reports for those addresses note the gap explicitly rather than silently returning Low.
We do not replace a professional survey.
For permits, financing, or insurance underwriting, a licensed geodetic or geotechnical engineer is still required. CheckHazard surfaces the right questions — it does not answer them with the authority a permit reviewer or underwriter requires.
Sources: UP NOAH Center · DOST · PHIVOLCS · GEM · MGB-DENR · NAMRIA · OpenStreetMap. Elevation data sampled from NASA SRTM 30m via OpenTopography.