polygon — the shape of the site

polygon /zone-path x,y x,y x,y …

polygon writes the shape of the site directly, as a list of vertices in mm. It is the one place in the notation where a shape is written out of free vertices that do not ride the grid.

In koyu a shape is normally something generated — the region of a space is written as rectangles of grid references, and walls, columns and roofs all follow from it. But the shape of a site is a given, coming from survey, not something the design produces. So it is admitted as the exception.

polygon /site -2600,-7000 38000,-7000 38000,19600 2000,21000 -2600,15000

Three or more x,y pairs. The coordinate system is the grid's: millimetres, X east-positive, Y north-positive. Negative values are fine.

It corresponds to a zone with site:1

The first positional argument is the path of a zone. Where that zone carries site:1, the polygon becomes the subject of the koyu site question. Where no such zone exists, you get a warning.

⚠ No zone corresponds to polygon /siteX

koyu 1.0
name 敷地の最小例
unit mm
grid X 0 8000
grid Y 0 6000
level L1 0 h:2700 slab:200

zone /site name:敷地 site:1 area:154.00
space /site/house room X1..X2 Y1..Y2 level:L1 name:建物
space /out/road exterior name:前面道路 road:6000

polygon /site -2000,-2000 12000,-2000 12000,9000 -2000,9000

boundary /site/house /out/road edge:S t:150
  door w:900 name:玄関
boundary /site/house /out/road edge:N t:150
boundary /site/house /out/road edge:E t:150
boundary /site/house /out/road edge:W t:150

Site /site (敷地)
  Site shape: polygon with 4 vertices (a polygon declaration — given geometry)
  Site area: declared 154.00 m2 / derived 154.00 m2
  Road: /out/road (前面道路) width 6000mm / frontage 28000mm
  Building footprint (horizontal projection, rough): 48.00 m2 → building coverage ratio 31.2%
  Total floor area: 48.00 m2 → floor area ratio 31.2%

What comes out of it

Derivation	What it feeds
area (shoelace)	site area, reconciled against the zone's area: (the surveyed figure in m2)
the outline	the check for a building escaping the site
the site boundary line	the site plan — drawn on the lowest storey's plan as a chain line

The site question still answers without a polygon — the site area is then derived from the union of the spaces inside the site and the indoor footprint. A polygon replaces that with the surveyed shape.

check speaks for the shape, validate for its relation to the building

A broken shape cannot produce a form, so that much belongs to reading the source, and check sees it.

Code	Severity	What it says
SIT01	error	a duplicate vertex in the site shape
SIT02	error	the site shape is self-intersecting
SIT04	warning	a polygon with no corresponding zone

✖ The site shape has a duplicate vertex (12000,-2000)
✖ The site shape is self-intersecting (near 5000,3500)

Judgements about the building's relation to the site live on the other side, as two rules of koyu validate.

Rule	Level	What it says
site.escape	violation	the building escapes the site shape
site.area	caution	the declared and derived areas disagree (tolerance ±0.05 m2)

✖ [site.escape] esc.muro:line 8: /L1/house escapes the site shape (near 0,0)
⚠ [site.area] site.muro:line 8: Declared and derived site areas disagree: declared 150 m2 / derived 154.00 m2

The escape test reads the derived region, not the written allocation. So an outline cut back to follow the site with a drawn line passes here. Spaces of type:exterior, and spaces beneath that polygon's own zone path, are left out of the test.

Keep it in its own layer

The standard practice is to put the site shape in its own file and stack it with import. Survey givens and design decisions are easier to follow through history when they are separate layers.

import ./site-geometry.muro

Writing polygon twice for one path is a build error, across composed layers as well as within one file.

To look a code up by cause and cure, there is the list of diagnostic codes.

Neighbouring pages

• zone — what a polygon corresponds to
• space — what is placed inside the site
• line — the other written shape
• koyu site — answers the site question
• koyu validate — speaks about escapes and area disagreements