Land Parcels Map Block for Svelte

Each chosen parcel contributes its four edges, named by the two lattice vertices at their ends. An edge that appears once is on the boundary of the site and an edge that appears twice is shared by two chosen parcels, so only the first kind is drawn. The result is one path made of segments, which is why the outline follows the union exactly even when the parcels are irregular.

Two parcels are neighbours when they share two lattice vertices, a whole edge. A breadth-first walk starts at the first chosen parcel and follows neighbours inside the chosen set; the site is contiguous when the walk reaches every chosen parcel. Parcels that meet only at a corner share one vertex and are not joined.

Edit LINES: a lattice cell, a lot name, a zone letter, the area in tenths of an acre and 1 when the parcel is for sale. Add a zone to ZONES. In your app replace the lattice with your cadastral polygons; keep the idea of counting edges by their end points, which only needs shared vertex ids.

Yes. Every parcel is a native checkbox in the list, which is a scroll region of its own, and the Clear button and the switch are ordinary controls. The parcels on the map are skipped by the Tab key and hidden from assistive technology. A polite message gives the area, the zone mix and the contiguity once the choice settles.

All of it. The parcels are invented sample data, not a survey, and nothing is bought, filed or saved. In your app send the chosen ids to your parcel or deal service when the site is final.

The switch sits above the map, which keeps its full width and a fixed height. The site card and the list of parcels stack under it, and the list scrolls in a box of its own so adding parcels never changes the page's height.