site-context-screen

Site context screen

A first look at one location from the layers Virginia publishes statewide. Every answer here is what one published layer holds, and the gap between that and what is on the ground is the whole subject of this walk.

1. Establish the frame

Resolve the government first, and get to a point.

Most of these layers are queried by coordinate rather than by parcel, so the walk needs a point. When the caller gives an address, geocode it. When they give a parcel ID, look the parcel up first: the parcel polygon is what defines "on this ground", and the building step uses it rather than a radius when it is available.

A radius covers a circle of ground, which a property is not. When the walk falls back to one, say so in the answer: a caller who asked about a single lot and gets everything within 250 m has been answered a different question.

2. Minimum data walk

Ask for what the question needs, in this order, and stop when it is answered. Running all four every time is the anti-pattern this walk is built to avoid.

Step 1 — parcel.lookup, when there is a parcel ID. Gives the polygon the rest of the walk can use. Skip it when the caller gave a point and did not ask about a parcel.

Step 2 — building.lookup. Whether the ground is built on, and how much of it.

• A hit gives footprints. Height, storey, and class fields are often null, which means the publisher holds no value rather than zero.
• Area is published in Web Mercator, where area is inflated by roughly 1.6x at Virginia's latitudes. Both the publisher's figure and a converted approximation come back, each labelled. Use the labelled one and say which.
• Empty is not vacant land. Coverage of this derived layer varies by locality, and a missing footprint is most often a coverage gap.
• A dense query truncates, returning the inline records and a handle to the whole retrieved set. Report the count, and use the handle rather than treating the short list as the answer.