Plot Size Diagram — Reading Urban Grain from Tax Lots
The CADASTRAL panel draws lot boundaries. From lines alone, "this neighborhood is finely subdivided" or "that block is one big parcel" has to be read from line density by eye. The PLOT SIZE panel takes the same polygons and colors them by area instead. No new data source — the same parcels asked a different question — so it appears wherever the cadastral panel does.
Why the picture matters: in urban design and development planning, lot size is the size of the development unit. A district of 2,500-square-foot lots and a district of 40,000-square-foot parcels can share a zoning designation and still produce completely different buildings, different assembly problems, and different odds of redevelopment. Reading that from one map settles the character of a site early.
The bands — 1,000 · 3,000 · 10,000 · 40,000 sq ft
| Band | Roughly |
|---|---|
| under 1,000 sq ft | Slivers and remnant lots; older commercial cores. |
| 1,000–3,000 sq ft | The standard New York rowhouse lot — 25 × 100 ft = 2,500 sq ft — sits here, as do most brownstone and rowhouse lots on the East Coast. |
| 3,000–10,000 sq ft | Detached houses, small mixed-use, assembled storefronts. Individually developable. The common Los Angeles residential lot — 50 × 150 ft = 7,500 sq ft — sits here. |
| 10,000–40,000 sq ft | Mid-size commercial and apartment sites. A single project. |
| 40,000 sq ft and up | Just under an acre and larger: full-block office and residential sites, institutional and public land. |
The Korean edition uses square meters (100·300·1,000·3,000 m²). The breaks are not legal thresholds in either country; they are where the picture separates in the cities we looked at. Minimum lot sizes and subdivision rules live in local zoning, and that comparison should be made against the code itself.
Where the parcels come from
There is no national parcel layer in the United States — each jurisdiction publishes its own, with its own schema. The US edition uses New York City's MapPLUTO tax lots, the Los Angeles County Assessor's parcels, San Francisco's parcels (DataSF) Boston's standardized assessor parcels (MassGIS) Washington, DC's tax parcels and Cook County Assessor parcels in Chicago Miami-Dade Property Appraiser parcels in Miami and Dallas Central Appraisal District parcels in Dallas, Harris Central Appraisal District parcels in Houston, City and County of Denver assessor parcels in Denver, King County Assessor parcels in Seattle, City of Minneapolis assessor parcels in Minneapolis (Open Data DC) — in each city, the same lots behind building age and land use. The Assessor records each condominium unit as its own parcel stacked on the same footprint; those stacks are merged back into one lot, so a condo tower reads as one site, not hundreds. The Data sources page lists each dataset and its publisher.
Streets are not lots here — but they are in Korea
An American reader may find this section odd, but it explains a difference you will see if you compare the two editions. In the Korean cadastre roads, rivers and railways are parcels with their own land-use code, and if you do not filter them the long road polygons all fall into the top band and the street network renders as "large parcels". In a 1,640 ft circle on downtown Seoul, roads were 29% of parcels by count and 34% by area. The Korean panel grays them out.
US tax-lot layers generally exclude the public right-of-way, so the street grid shows up as blank between the lots — which is why a Manhattan plate reads as a white grid with colored fills, and a Brooklyn rowhouse block as stripes of 2,500-square-foot lots. Where a parcel layer does include right-of-way or rail parcels, the same gray treatment applies.
Count and area disagree
The first plates came out too dark, and the distribution explained why. Measured on downtown Seoul, but the shape is general:
| Band | Share of parcels by count | Share of area |
|---|---|---|
| smallest band | 57% | 5% |
| largest band | 2.5% | 44% |
By count, more than half the parcels are tiny. But area is what fills the screen, so a couple of per cent of large parcels cover nearly half the plate and the darkest color swallows it. We pulled the whole ramp lighter: five bands still, the top one less heavy.
The disagreement is itself information. Manhattan reads as fine lots with full-block parcels punched through; a rowhouse district reads as fine lots throughout. Put two neighborhoods side by side and the contrast is immediate.
Reading it with the cadastral panel
- CADASTRAL — boundaries. The exact shape of the site, its relation to neighbors, the unit of assembly or subdivision. The underlay in a layout.
- PLOT SIZE — area as color. The scale of development units across the whole neighborhood and how it is distributed. It answers "where is the grain fine and where is it coarse?"
In a report the two usually sit side by side, shape against scale.
What it cannot tell you
Ownership. Tax lots divide the ground; they do not merge adjacent lots held by the same owner. In New York in particular, a zoning lot can span several tax lots by agreement, so the development unit that zoning actually sees may be larger than anything on this map. Fine grain here does not mean assembly is hard.
Currency. Assessor and planning-department parcel files are published on their own cycles; recent subdivisions and mergers can lag. Areas are computed from the polygon and may differ slightly from the recorded lot area, so a lot near a band boundary can sit one band over.
Parcels whose land-use or class field cannot be read are left in the graded bands rather than grayed out. Better than silently dropping them: if one of them was a right-of-way, it shows up as a dark strip a reader can recognize.
How to read it
Three things to check when you first look at a site. First, which band the site itself is in — larger than its neighbors usually means it has already been assembled or was public land. Second, the dominant band around it — fine grain means an assembly or rowhouse logic; contiguous large parcels mean single-site development logic. Third, where the band changes abruptly — that line usually coincides with a zoning boundary or a major street, and when it does not, that is a question worth asking.