Environmental-risk overlay

Constant `'Layer'` on property risks — a placeholder marking these as map-layer hits rather than statistics for a suburb or region. It is not a geographic level and carries no information; the suburb risk endpoints use this slot for a real one.

Constant `'Risk Layer'` on property risks. Like `area_level`, a placeholder that keeps the row shape consistent with area-based responses — not the name of any actual area, and not the name of the hazard (that is `name`).

Which hazard this record is about — a fixed label per overlay, e.g. 'Fire', 'Flood', 'Historically Flooded', 'Landslide', 'Erosion', 'Heritage', 'Environment', 'HV Power Line', 'Mobile Black Spot', 'Public Housing'. Suitable for display as-is.

A display string summarising this record. On hazard overlays (fire, flood, landslide, erosion, heritage, environment, power lines, black spots) it states the containment result in words — `'On property'`, or `'Not on property; nearest 174 m away'`. It is prose for humans: parse `on_property` and `nearest_distance_m` instead. On public-housing records it is instead a preformatted percentage such as `'3.4%'` (see `value_unit`). Do not parse it as a number without checking `value_unit` first.

**Whether the hazard actually covers this property**, as opposed to merely existing nearby. True when a feature of this overlay contains the property's address point. This is the field to gate any 'this property is in a flood/bushfire/heritage zone' statement on — record presence alone only means 'found within `search_radius_m`'. Two overlays are line/point data rather than zones — HV power lines (`'HV Power Line'`) and mobile black spots (`'Mobile Black Spot'`) — and for those `on_property` is false for every property by construction; `nearest_distance_m` is the signal there. On public-housing records it marks the one Census area the property actually sits in.

Metres from the property's address point to the nearest feature of this overlay, measured geodesically and reported to the whole metre. `0.0` exactly when `on_property` is true. When `on_property` is false this is how far away the hazard really is — a heritage record at 174 m and one at 950 m are both 'found', and only this field separates them. On public-housing records it is the distance to that record's Census area. Accurate to about 2% and biased very slightly long (it never under-reports the gap); at close range the error is sub-metre.

The radius searched around the property, in metres (1000). Any record you receive was found inside this circle; anything beyond it was not looked for. Present so the presence rule is explicit rather than folklore.

How many features of this overlay fall inside `search_radius_m`. Separates 'one stray polygon clips the corner of the neighbourhood' from 'the whole area is mapped'. Absent on public-housing records, where each record already is one Census area.

What `value` is measured in, and the flag for whether it is a number at all. Null on hazard overlays, whose `value` is the containment sentence. `'Properties Proportion'` on public-housing records, meaning `value` is the share of dwellings in a nearby small Census area that are public housing, written as a percentage string. Public housing can return several records — one per nearby Census area that clears a minimum share — so expect a list, not a single figure.

GeoJSON FeatureCollection of the hazard polygons for this overlay, ST_Intersection-clipped to a 1km-radius circle around the property and simplified for browser use. Present only when the request passes `?geojson=true`; absent (and the response byte-identical to before) otherwise.

Clip / simplify / truncation metadata for `geojson` (clip_method='1km_radius', radius_m, simplify tolerance, coordinate precision, feature/byte caps, and whether the size cap truncated the output). Present only with `?geojson=true`.