← BARC History Project
# BARC pixel map: sources and method
The map at `/map` is a raster illustration built by rule from public data. It
is a visualization aid, not a land-cover survey.
## Sources
| Layer | Source | Date | Licence |
| ------------------------------- | -------------------------------------------------------------------------------------------------- | ------------- | ---------------------------------------------------- |
| Property boundary | Maryland iMAP parcel geometry, principal components over 20 acres | 2026 handoff | Maryland open data |
| Ground cover | Chesapeake Bay Land Use/Land Cover database, 2024 edition, 2021 epoch, 1 m, Prince George's County | 2021 imagery | CC0 (USGS ScienceBase item 68011be0d4be0263cab0ff61) |
| Roads, rail, streams, buildings | OpenStreetMap | 2026 snapshot | ODbL |
| Landmarks | OSM building anchors for the National Agricultural Library and the George Washington Carver Center | 2026 | ODbL |
## Method
1. Each map tile at zooms 12, 14, and 16 is a grid of cells 29.7 m, 7.4 m, or 1.9 m wide.
2. The land-cover raster is resampled to that grid by nearest neighbour and reclassified to eight terrains (table below).
3. Cells outside the property boundary become paper.
4. The boundary, streams, roads, rail, and building footprints are burned into the grid in that order, at widths fixed per zoom.
5. Terrains are dithered between two shades with a Bayer matrix keyed to world cell coordinates, so the pattern does not move when the map pans.
6. Woodland, wetland, and water get a one-cell dark rim where they meet another terrain. Buildings get a one-cell shadow to the east and south. Rail gets a tie every third cell.
Zoom is restricted to whole levels. Each drawn zoom is also shown one level higher at exactly twice the size.
## Reclassification
| LULC classes | Terrain |
| --------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------- |
| Tidal waters, lakes, ponds, streams (10–14) | water |
| Roads, structures, other impervious, canopy over impervious, bare developed, extractive and solar impervious (20–25, 28, 31, 32) | developed |
| Tree canopy over turf (26), shrubland classes (35, 38, 44) | scrub |
| Turf grass, bare shore, barren and herbaceous succession, solar and extractive herbaceous, pasture and hay (15, 27, 30, 33, 34, 36, 37, 42, 43, 45, 46, 85, 86) | open |
| Forest, forested other, forested wetlands (40, 41, 53, 54, 63, 64, 73, 74) | woodland |
| Barren, herbaceous, shrub, and harvested wetlands (50–52, 55, 60–62, 65, 70–72, 75) | wetland |
| Cropland, orchards, vineyards (80–84) | cropland |
| No data (0) | paper |
## What the map does not claim
- No interior farm divisions. The five named farms of the 1996 master plan have documented names and approximate positions but no surveyed boundaries, so none are drawn.
- No crop types. Cropland is one colour.
- The detached 19-acre parcel to the northeast is part of the property but outside the drawn frame.
- OpenStreetMap coverage of internal service roads and buildings is uneven; absence on the map is not evidence of absence on the ground.