The 3D model on the Building Mass sheet is not only for spinning on screen. Terrain, buildings, green space, water and roads can be downloaded together and used as a context model in your design software — replacing the hour spent extruding the neighbours one by one before a massing study can start.
There are three formats. Which one you want is decided by what will open it.
| Format | Opens in | Character |
|---|---|---|
| GLB | Blender · Twinmotion · Unreal · web viewers · most 3D tools | The most widely readable. Mesh-based, so better for rendering and visualisation than editing. |
| 3DM | Rhino · Grasshopper | Buildings arrive as solids (extrusions), ready for boolean, offset and editing. Layers by use. |
| SKP | SketchUp (Pro · Go · Free web included) | Each building a group, with layers and materials by use. Opens by double-click or File ▸ Open. |
All three carry the same content: buildings (coloured by use, age or height), a terrain surface from the contours, and green, water and road faces. A 500 m circle on Manhattan is about 6.5 MB.
The SketchUp export used to be COLLADA (.dae). Users kept reporting that it "would not open". The files were valid — they passed schema validation — but two things were going wrong. SketchUp Free (the web version) cannot read DAE at all; the format table lists it as Go and above. And even in Pro, DAE has no file association, so double-clicking does nothing, and the File ▸ Import dialog defaults its filter to *.skp so the file does not even appear in the list. Anyone would conclude it was broken.
.skp is a proprietary format and the official SDK has not been publicly available since May 2026, so we assumed the door was shut. It was not: an open-source library (MIT) has reverse-engineered the format and reads and writes it without the SDK. We use it to write SketchUp 2017-format files. SketchUp opens every older version, so the file opens from 2017 through current releases, and Free opens it too. Because it opens by double-click, the import instructions became unnecessary, and the DAE button was removed.
On the Building Mass sheet, buildings can be coloured by use, year built, height, or a single colour, and the palette can be edited. The downloaded model carries exactly the colours on screen at that moment: in age mode, pre-war buildings dark and new ones pale; in height mode, low-rise light blue and towers navy; if you changed a palette entry to red, the material is red.
| Mode | SKP materials | 3DM layers |
|---|---|---|
| Use | up to 10 | Buildings-Residential, Buildings-Office … |
| Year built | 6 bands + unknown | Buildings-1980s … |
| Height | 5 bands | Buildings-25–45 m … |
| Single colour | 1 | Buildings |
The mode is written into the filename (sitedia_3d_age_…skp) so a use-mode
file and an age-mode file do not overwrite each other.
Under the hood, the browser sends the band edges, colour ramp and labels, and the server only interprets them. If the server kept its own rule for "what counts as the 1980s", it would eventually drift from the screen, and you would download colours you did not see.
The first SKP release drew "buildings with no colour" reports. Inspecting the file, all fifteen materials were present and every one of 25,833 faces had a material on its front side. Colour was innocent. The faces were inside out. SketchUp paints front and back separately and the default back-face colour is white: seen from outside, the back face hid our colour on the inside. 433 of 433 buildings were flipped.
The cause was footprint rings whose winding direction was not guaranteed (in practice mostly clockwise). It was fixed at the one place rings are built, by normalising them counter-clockwise. The 3DM exporter had quietly fixed the same problem for itself, which is why the bug in the shared function stayed invisible for months. As insurance the SKP now paints both sides of every face — if a face is ever flipped it no longer shows white — at zero cost in file size.
SKP files downloaded before 2026-09-03 are the old kind and still render white. Download again.
The largest limitation of the 3D export. Building footprints come from Overture Maps
and are extruded using Overture's height or, failing that, num_floors.
Where neither is present, the building cannot be built: it exists in the 2D plates
as a footprint but not in 3D. Coverage varies by city and neighbourhood, and we have not
measured the share for US cities the way we have for Seoul (about 21% there).
Because the tool does not invent data, there is no "extrude at average height" fallback. A missing building stays as a footprint telling you where something needs a height, and you supply it from assessor records or a site visit.