The whole Commonwealth is laid on the inside of a spinning cylinder at one to one. The map frame is Massachusetts State Plane metres (the same grid the Webster drive uses), so a metre driven here is a metre there. East to west runs down the axis. North to south wraps around, which is why the land climbs the walls and the far side hangs overhead.
| Radius | 30.0 km at sea level |
| Length | 329.9 km, Berkshires end to Atlantic end |
| Around | 188.5 km, of which the state's 182.2 km north to south leaves a 6.3 km seam |
| Windows | 37% of the hull is glass, where New York, Vermont, New Hampshire, Connecticut and Rhode Island would be (O'Neill's Island Three alternated strips of land and window). Through it the sky turns once every 5 min 47 s. The habitat is drawn at L5, so the Earth is 1.9° across and the Moon half a degree, sixty degrees apart. |
| Spin | one turn every 5 min 47 s gives 1 g at sea level, and the ground moves at 542 m/s |
| Weight | Falls with altitude (about 3.5% lighter on Greylock) and changes when you drive with or against the spin: north is spinward here, so 65 mph north adds about 11%. |
| Air | Thins toward the axis as spin gravity fades. The blue overhead is real scattering through about 24 km of sea-level-equivalent air. |
| Sun | A lamp that rides the axis from the Atlantic cap at 6 to the Berkshire cap at 18, so it is noon under it and evening far from it, all at once. |
| Elevation | Near you the ground is the bare earth of the LiDAR surveys (the ones the buildings and trees come from, below), read onto nodes 8 m apart. Farther off it is USGS 3DEP 1 arc-second elevation (about 30 m) on a 46 m grid (92 m on phones). No vertical exaggeration. On the LiDAR ground Greylock's summit comes out at 1,064.4 m against a surveyed 1,063.4 m, and Mount Tom at 365.5 m against 366.4 m. |
| Streets | Every public road in OpenStreetMap: about 68,000 km and 57,000 names, with one-way carriageways and lane counts where they are tagged. Each street's paved width (travel lanes and shoulders), lane count and sidewalks come from MassDOT's road inventory where it lies along an inventory segment (about 150,000 ways; the rest keep a width by class and lane count). A street's height is the LiDAR ground under it, read every 4 m along its length. HOV-only lanes and ramps closed to cars (the Southeast Expressway's zipper lane among them) are left out, and where the two carriageways of a divided road lie closer together in the map than their lanes are wide, both are narrowed until they just meet. |
| Bridges | About 8,500 stretches of road and track that OpenStreetMap tags as bridges (7,250 on streets, 1,290 on railways) stand at the height the LiDAR measured for their decks, which it did for 95% of their length. The Sagamore Bridge crosses the canal 46 m up and the Bourne Bridge 45 m up, the Braga Bridge is at 47 m, and the Tobin's upper deck runs from 45 to 53 m. An overpass passes over the road beneath it. The Federal Highway Administration's National Bridge Inventory (2025) is matched to 4,651 of its 5,311 Massachusetts structures: each matched bridge takes its design and material (slab, girder, truss, arch, suspension, cable-stayed, movable), and a girder bridge's beams are as deep as its longest span calls for. |
| Rails, runways, rivers | OpenStreetMap again: about 3,300 km of railway track on the surface (sidings and yards included), 114 km of runways and 214 km of taxiways at their tagged widths where they have one, and the centre lines of about 1,470 km of river too narrow to appear in the water map. |
| Buildings | 2.67 million OpenStreetMap footprints (mostly from MassGIS). About 2.29 million of them stand on their real outlines with measured roofs: rectangular sections in the building's own frame, each under a few planes fitted to the LiDAR's roof returns at up to four a square metre, which is how and how finely the Webster drive measures its roofs. Wall heights and storey counts there follow the measured eaves. The rest (mostly sheds and small garages with too few returns, and buildings newer than the survey) are still rectangles fitted to their outlines. About 5,400 fits did not hold up and were thrown out, so those buildings are rectangles too. Nearly all were small buildings under tall trees, which the fit had turned into thin towers. About seventy came out 45 m tall or more outside the cities with no tagged height to back that up. Some of those stood in a strip west of Worcester where two of the surveys meet and stray returns high above the ground were read as roofs, and a few sat under what was probably low cloud on Nantucket. |
| Assessor records | MassGIS's standardized assessor parcels for every city and town but Boston (which publishes its own and is not in that set yet). The 1.78 million footprints that stand on a parcel with a record take its use, building style, storeys and year built: a single-family house the assessor calls a Cape is a Cape, a three-family of three storeys is a triple-decker, a mill is a mill, and a Dutch colonial gets its gambrel roof. A record describes a parcel's main building, so the smaller footprints on a house lot are its garages and sheds. |
| Boston and Cambridge | The cities' own assessing records (Analyze Boston's property assessment for 2026 and the Cambridge Property Database), joined to about 117,000 buildings through the cities' parcels: each building's type, storeys and year built, its roof shape (a mansard is drawn as a gambrel) and what its walls are (brick or stone, wood or vinyl siding, wood shingles, stucco, concrete, glass or metal). |
| Roof colours | The MassGIS 2025 aerial (leaf-off, about 0.44 m a pixel as read here): each footprint's roof colour is the median of the pixels in the middle of its outline, leaving out leaves, shade and glare, mapped to roofing albedo the way the Webster drive maps it. Buildings taller than about 25 m lean in the photograph, so their roofs keep a colour drawn by rule, as do roofs the reading could not see. |
| Trees | The trees within about 30 m of a street or 40 m of a building are the ones the survey found, 15.8 million of them: the tops of its canopy height grid (2 m cells), each at its measured height. About 2,000 of the measured "trees" stood far taller than the woods around them and were left out (they were most likely masts, cranes, bridge towers and stray returns, and about 650 of them sat in what looks like a low cloud over Nantucket). Deeper in the woods the trees are placed to match the canopy cover and canopy height the LiDAR measured, on a 31 m grid. |
| LiDAR | USGS 3DEP point clouds: the 2021 survey for central and eastern Massachusetts, and surveys from 2011 to 2015 for the west, the coast and the islands. A building or tree newer than its survey is estimated or missing, and a road built since runs over the ground as it was. |
| Water | OpenStreetMap lakes, ponds and river polygons (about 12,700 still waters) and its coastline. Surface levels are read from the USGS elevation, which is flattened over water. |
| Land cover | Within about 2 km of you, NOAA's high-resolution land cover at 1 m (C-CAP, from 2016 imagery): paving and roofs, lawns, crops, hay and pasture, grassland, broadleaf and evergreen woods, scrub, wooded and shrub swamp, marsh, beach, bare ground and small ponds, each where it was in 2016. Woods among lawns and paving are drawn as yard trees over grass. Farther off, NLCD 2025 land cover and tree canopy at 30 m: built-up land, canopy percentage, the evergreen share of the forest, cropland, pasture, marsh, sand and bare ground. |
| Town lines | US Census Bureau cartographic boundaries, 1:500,000, 2022 (all 351 cities and towns). |
| Dunkin' | All the Places (alltheplaces.xyz), its copy of Dunkin's own store locator, October 31, 2026: 1,025 shops in Massachusetts. |
| Webster | Ground heights inside the town come from the Webster drive's own LiDAR terrain (MassGIS). Its streets, buildings and trees are drawn the same way as every other town's. |
Where a building is not measured, its height is estimated: about 26,000 footprints carry a tagged height or storey count and eleven named towers carry their surveyed heights, and the rest are sized from the footprint, the kind of building and how built-up the surroundings are. Where there is no assessor's record (in Boston, and for footprints on no parcel), the kind of building (house, cape, ranch, triple-decker, rowhouse, shop, mill and so on) is guessed from the footprint's size and shape, its OpenStreetMap tag where it has one, and its neighbours. The front door goes on the side nearest a street. Outside Boston and Cambridge a wall's material is drawn by rule from the kind of building, its age and where it stands (wood shingles are commonest on the Cape and the Islands). Siding, trim, door and shutter colours are drawn by chance from the Webster drive's reads of 4,775 assessor photographs of its houses, so the mix of colours is Webster's and no one house's is its own. Windows, doors and chimneys are placed by rule, in the manner of the Webster drive and with its surface textures, and so are roof shapes and porches where the roof is not measured. A measured roof is simplified: anything smaller than about a metre is left out. Where the fit has a roof rising more steeply than a roof can (it happens on glass towers, where returns come off the walls and through the glass), that part is drawn flat. The chimneys and dormers on it were not measured, they are placed by rule (dormers go on most capes and a few other houses). Where the LiDAR saw no canopy to go by, the trees away from streets and buildings are scattered to match the land-cover canopy percentage. A measured tree keeps its place and its height, and it is evergreen or broadleaf as the 1 m land cover under it is (a guess where that shows no woods, and the land cover is from 2016). Its crown is one of two stock shapes scaled to that height. Sidewalks and kerbs are drawn on both sides of every street that MassDOT's inventory gives a sidewalk on either side, where the land is at least a little built up; their width and the grass strip behind the kerb are invented. On cropland in the 1 m land cover, the colour (green with its crop, tilled brown or ripe gold) is drawn by chance in patches about 200 m across, which are not the real fields. Road widths come from the road class and lane tags. Utility poles, their wires and the street lamps that some of them carry, parked cars, front walks, driveways and the cars on them are placed by rule along streets and beside houses, and none of them is surveyed. The traffic is invented too: cars follow the mapped streets at about the speed limit, keep to the right, and pick a road at random where theirs ends. Buildings and other cars are solid. The boats are invented as well: sailing boats, launches and fishing boats wander wherever there is water enough, and ferries run between sixteen pairs of real terminals (Woods Hole and Vineyard Haven, Hyannis and Nantucket, Boston and Provincetown and so on) along the shortest path through the water map, which is close to the real course and is not it.
A street's height is smoothed along its length so that a road keeps a road's grades, and a bump in the survey that is really a bridge passing overhead is ignored. A bridge's deck is at its measured height and everything else about it is invented: the parapets, the slab, the piers (one every 30 to 120 m, farther apart under a high deck) and the lamps. Where the National Bridge Inventory says a bridge is a truss, an arch, a suspension or cable-stayed bridge or a lift, bascule or swing span, that structure is drawn by rule from its design and the length of its main span, so the Sagamore and the Bourne have their arches and the Zakim its towers and stays, but the members are not measured. Where one deck runs under another for a long way, as the Tobin's lower deck does, it is set beneath the upper one by the gap measured where it comes out from under it. About 390 more spans that the map does not tag were found where the surveyed ground drops away under a road, and their decks are smooth curves from rim to rim because nothing was read for them. A road tunnel runs underground, but only its route is real: its floor goes down from each portal at up to 5.5% to about 10 m under the ground over it (24 m under the harbour), the roads leading to a portal come down to it in a cut, and the tube, its lamps and walkways and the headwalls round its mouths are invented. Railway tracks stop where the real line goes underground. A river narrower than about 50 m is drawn as a channel 8 m wide unless its width is tagged, which is rarely its true width, and streams are not drawn. Each railway track is drawn as one track on ballast. Runway and taxiway paint and lamps are generic. In the distance, where the ground is the 46 m grid, detail finer than the grid has about a metre and a half of invented texture. The ground eases down to the water along every shore over a band at least 30 m wide, so a bluff or a steep river bank is gentler here than the real one. Past the state line the neighbours' land runs on for about 460 m and falls to a border sea about two kilometres wide, then a quay, then the glass. The Atlantic and the bays and sounds off the coast are sea, as they are. The window's frame (girders every 6 km, beams every 750 m, glazing bars every 50 m) is invented, and so are the lamps along the quay and the lifts and marker lamps on the end caps. The stars are scattered at random and are not the real sky, the Milky Way (its bulge, its dust lanes, its star clouds), Andromeda and the Magellanic Clouds are painted by formula and are not where the real ones lie, and the faces of the Earth and Moon are invented. So is the twin: O'Neill's cylinders were meant to come in pairs turning opposite ways, and a second one rides 135 km off, so its windows and the lights of its towns wheel past ours once a rotation. You can drive on the glass.
Retaining walls along the cuts, streams, lighthouses and the surveyed ferry courses.
Data: US Census Bureau, USGS, MRLC, NOAA, FHWA, MassGIS and MassDOT (public domain), the City of Boston and the City of Cambridge (open data), All the Places (CC0) and OpenStreetMap contributors (ODbL).