Free parcel data in District of Columbia

Yes. District of Columbia publishes a free statewide parcel layer: Owner Polygons (Common Ownership Layer), from DC Office of the Chief Technology Officer (DC GIS). Coverage: Entire District (all land outside right-of-way). It's a public ArcGIS REST service with no API key or login.

The layer

Layer	Owner Polygons (Common Ownership Layer)
Publisher	DC Office of the Chief Technology Officer (DC GIS)
Coverage	Entire District (all land outside right-of-way)
Data vintage	OTR extract up to 2026-10-16 (EXTRACTDAT)
Terms	Public; attribution: District of Columbia (DC GIS / OCTO)
Fields	parcel number (SSL); site address (PREMISEADD); owner (OWNERNAME); deed reference
Not published	plat references
REST endpoint	`https://maps2.dcgis.dc.gov/dcgis/rest/services/DCGIS_DATA/Property_and_Land_WebMercator/MapServer/40`
Last verified	2026-10-19 with a live point and parcel-number query

Notes for GIS users

SSL (Square-Suffix-Lot) is fixed-width with padding spaces: 4-char square, 4-char suffix, 4-char lot, e.g. '0255 0800'; normalise user input before matching. Built from record, tax, parcel, reservation and air-rights lots. Tax Lots alone are layer 39.

How to use it

QGIS: Layer > Data Source Manager > ArcGIS REST Server, add a connection with the service URL (the endpoint above without the final /0), then add the layer. Filter to your area before exporting.
ArcGIS Pro: Add Data > Data From Path, paste the endpoint.
Direct query: append /query?geometry=LON,LAT&geometryType=esriGeometryPoint&inSR=4326&spatialRel=esriSpatialRelIntersects&outFields=*&f=geojson to get the parcel at a point.
CAD: see getting a parcel into AutoCAD or Civil 3D.

Assessor parcel lines are for taxation and are often 5 to 50 ft off the legal boundary. Why.

Basesheet uses this to draw the parcel line on a base plan for any District of Columbia address, with LiDAR contours, soils, flood zones and wetlands.

Build a base plan