District of Columbia property research



Official DCGIS common-ownership layer retrieved September 23, 2026. Source extract timestamps are retained per record and vary. CY1YEAR is a current-year description, not a certified assessment fiscal year. Snapshot IDs are not persistent cross-vintage identifiers; original SSL and GLOBALID are retained. The common-ownership geometry covers source lots outside right-of-way and does not represent individual condominium-unit boundaries.



Attribution: District of Columbia, Office of the Chief Technology Officer GIS and Office of Tax and Revenue, Vector Property Mapping and Integrated Tax System Public Extract.

Source: https://maps2.dcgis.dc.gov/dcgis/rest/services/DCGIS_DATA/Property_and_Land_WebMercator/MapServer/40

Reuse: Creative Commons Attribution 4.0, as stated in official DCGIS layer item metadata. Retain attribution, license and an indication of transformations; no endorsement implied.

https://creativecommons.org/licenses/by/4.0/



These are dated research files, curated from public source facts. Ownership is an assessor entry, not verified legal title or a statement that a property is for sale. Source and import dates differ; September 2026 enrichment does not refresh the underlying assessment or ownership record.



GEOGRAPHY: Every retained valid parcel's representative point is tested against the official Census ACS 2024 county boundary with a 100-meter boundary tolerance. Valid source geometry is preserved. Where explicitly documented in GEOMETRY RECOVERY below, exact duplicate rings may be removed with the original geometry retained as evidence. Unrecoverable geometry receives null analytical results. Parcel record count describes the imported selection, not a guarantee of all current parcels. Distinct identifiers are retained even when geometries overlap (for example condominium interests).



FLOOD: Full valid parcel polygons intersect official FEMA NFHL flood-hazard polygons. Union areas avoid double counting; intersections smaller than one square meter are omitted. Percentages use the full parcel area as denominator, with coverage recorded separately. Special Flood Hazard Area means SFHA_TF=T. Coverage below 99.9% leaves an unknown remainder, not a negative flood finding. Zone X and zero mapped SFHA do not certify freedom from flooding. This is screening data, not a flood certificate, survey, insurance recommendation or engineering opinion.



SCHOOLS: NCES 2024-25 physical active public-school points and Census ACS 2024 unified-school districts. Nearest school is shortest parcel-to-point straight-line distance among retrieved physical schools in the state. It does not determine attendance eligibility, walking distance or school quality. Verify enrollment with the district.



ZONING: Where present, zoning is copied from an original assessor attribute. The original base parcel fields contain no zoning-polygon result; use zoning-review.csv and its evidence for the separately supplied measured zoning layers. No permitted-use verification is performed. Blank means unavailable. Land use is the original tax classification, not a permitted-use conclusion. Utility service/capacity, development approval, road access, title and survey boundaries are not established by these files.



DATA HANDLING: Zero remains distinct from missing. Blank, UNKNOWN and punctuation-only address placeholders become null. Original source field names and dates are documented. Invalid source parcel geometry is not silently repaired; invalid overlay geometries may be repaired for intersection and counts are documented. Owner names and public tax mailing addresses only; no personal phone/email enrichment or demographic profiling.



USAGE: Paid curation of nonexclusive public facts; internal business and client work are allowed. Attribution is retained. LandSight claims no exclusive rights to government facts. Seven-day correction/refund policy if delivered files fail their stated scope: dakota@landsightsolutions.com.



DC FIELD MEANINGS: LANDAREA is square feet according to the official ITSPE Owner Polygon dictionary (MapServer66); computed_screen_acres is a separate polygon calculation. STATEDAREA and its original unit-domain code are retained separately and not substituted for LANDAREA. ASSESSMENT is current assessed total; PHASELAND/PHASEBUILD are current land/build values. These are source assessor values, not an appraisal or market value. Source SALEDATE epoch milliseconds are preserved; recorded_sale_date is their explicit UTC ISO rendering. Zero sale price is retained and not interpreted as a market transaction. EXTRACTDAT is a database extraction timestamp, not title verification; LAST_EDITED_DATE is a feature edit date. CY1YEAR is retained as a description; assessment fiscal year remains unknown. USECODE and PROPTYPE are source classifications, not zoning permission. CITYSTZIP is preserved as a combined tax-mailing line; no city/state/ZIP split is guessed. Mailing field presence is not deliverability or occupancy.

SOURCE SCOPE: The original response archive contains all retrieved source records and 48 explicitly listed original fields, with original geometry. It does not contain all columns in the public table. Selected source fields omit tax balances, penalties, mortgage and homestead information. Original record keys and metadata are included. Common lots can repeat an SSL; duplicate source IDs are not discarded or conflated. Individual condominium interests and approval relationships require separate review; a parent-lot boundary must not be represented as a unit boundary. These research records do not establish legal title, current sale availability, access, entitlement or development feasibility.

SOURCE LICENSE: Underlying DCGIS source data are licensed CC BY 4.0, https://creativecommons.org/licenses/by/4.0/. Attribution: District of Columbia OCTO GIS, Office of Tax and Revenue and originating agencies identified in source metadata. LandSight normalized selected attributes, rendered sale-date timestamps, measured spatial overlays and added source/coverage flags. No government endorsement is implied. The underlying CC BY rights remain available and are not restricted by LandSight's paid curation terms.



DC PROJECTION ACCURACY: Analysis-only parcel and FEMA geometry is densified to a maximum 0.0001-degree segment before projection. This avoids artificial slivers caused by projecting long straight source edges. Original output parcel geometry and source archives remain unchanged. Independent QA uses EPSG:6933 and 0.00005-degree densification with a convergence check; the 0.025-percentage-point agreement gate is unchanged.



Projection for measured areas/distances: EPSG:26918

NATIONAL WETLANDS INVENTORY SCREENING
Source: U.S. Fish and Wildlife Service, National Wetlands Inventory, national public REST services, retrieved 2026-09-23T21:21:05.237360+00:00. Imagery years vary and are retained per parcel; the download release or retrieval date is NOT the imagery date. NWI maps wetland and deepwater habitat using biological definitions. Mapping does not establish regulatory jurisdiction or show every wetland. No mapped overlap is not a certification that wetlands are absent.
Full valid parcel polygons are intersected with NWI polygons in their native equal-area EPSG:5070 projection. Overlap uses the union of intersections of at least one square metre. Original parcel geometry and all prior fields are preserved. Invalid parcel geometry remains analytically unknown. Project coverage is limited to the reconciled county query extent. Parcels extending beyond the retrieval extent are marked unknown.
nwi-evidence.ndjson retains matched NWI identifiers, codes, types and parcel overlap shares. nwi_project_coverage_pct measures retrieved digital project footprint coverage, not the accuracy or completeness of real-world wetlands. nwi_imagery_years describes the mapped project imagery and can be old. Partial mapping is explicitly flagged.
Mapped area outside SFHA counts only the FEMA-mapped portion outside SFHA. It is NOT buildable acreage and does not subtract NWI wetlands, setbacks, access constraints, easements or other restrictions. Open parcel-screening.html locally to filter the CSV without uploading it.
Source documentation: https://www.fws.gov/program/national-wetlands-inventory/data-download
Limitations: https://www.fws.gov/page/national-wetlands-inventory-frequently-asked-questions

Evidence record_id refers to the original CSV parcel_id. No parcel identifiers or original values were replaced.


DC ZONING AND CONDOMINIUM REVIEW SUPPLEMENTS
Open dc-review.html to load either zoning-review.csv or condo-record-review.csv locally, filter review questions and export every matching row with all original columns. The workspace reads your file in the browser without uploading it. Online sample buttons require internet access; local CSV review works independently. These files use separate record identities and must not be added together as distinct land parcels. The parcel CSV and GeoJSON are preserved byte-for-byte from the verified wetlands pack.

ZONING: Join zoning-review.csv to parcels.csv by exact parcel_id. source_common_lot_object_id and source_ssl preserve original DC keys. The review intersects full valid common-lot polygons with the licensed DC Open Data final zoning layer 32 and separate overlay layer 6, retrieved September 23, 2026. A 2016 dataset title identifies the regulations, not the snapshot year. zoning_mapping_coverage_pct measures union coverage of retrieved zone polygons; full mapping means at least 99.9 percent. Matches smaller than one square metre are omitted. zone_labels contains every matched label; multiple_zone_labels flags a potential split-zone review. This flag is not a finding of a source error. inclusionary_zoning_designations retains source labels, not a determination that a specific project triggers an obligation. Overlay areas can modify base-zone standards. overlay_overlap_pct measures only retrieved overlay intersections and is not completeness of all special restrictions. No matches, partial mapping and invalid parcel geometry are distinct.
zoning-evidence.ndjson preserves every matched polygon's ID, original attributes, links and overlap share. zoning-provenance.json and zoning-coverage.json document dates and measurements. Analysis uses EPSG:26918 with independent densified EPSG:6933 checks. No source parcel geometry is repaired or changed. Official source geometry repairs are analysis-only and counted. This supplement does not include pending zoning, case-specific PUD conditions, air-rights determinations or an independently verified development-standards table. Confirm applicable regulations and case conditions with the Office of Zoning at https://dcoz.dc.gov/page/zoning-maps-district-columbia before relying on a project-specific use, density, height, setback or approval conclusion.

CONDOMINIUMS: condo-record-review.csv uses condo_record_id, not parcel_id. unit_ssl preserves the original tax interest identifier, including leading zeros and internal spaces. The published DC relationship rules are CondoRelate.SSL = ITSPE.SSL (relationship38), CondoRelate.REGIME = OwnerPLY.CONDO_REGIME_NUM (relationship11), and CondoRelate.MAT_SSL = CondoApprovalLots.SSL (relationship17). Blank keys never match. Exact strings only; no fuzzy correction. All matching source object IDs are retained as JSON arrays. Assessment attributes are populated only for one exact source match. Multiple matches can represent legitimate multi-lot regimes. No match does not establish an invalid unit. condo-relationship-review-queue.csv includes any record without a unique match in all three relationships. Review flags describe source relationships, not legal defects, fraud, title or sale availability.
To relate unique or multiple common_source_object_ids to the main parcel file, use source_object_id. A source record excluded from the main file for a location exception remains in the separately preserved original source and exception file. Never assign a parent-lot polygon as the boundary of an individual condominium unit. unit_geometry_status explicitly records this limitation. Source assessment extract dates, current-year descriptions, assessed values and recorded sale fields are dated source attributes, not verified current title or market value. Millisecond date fields retain original source units; zero sale prices are not presumed market transactions. Mailing fields do not verify deliverability or occupancy.
The four dc-*.csv exports contain all retrieved rows and the selected original attributes from related sources. The ITSPE export retains 25 selected neutral fields, not the entire public financial table; other retrieved sources retain the fields listed in their acquisition receipts. Original source response archives, metadata, licenses, counts and checksums are under research-sources/. The original common-lot source remains original-parcel-source.json.gz at the ZIP root. condo-provenance.json specifies exact joins. Every output row and original source-export value was independently checked using SQLite joins, with eight direct official queryRelatedRecords controls.

SOURCE RIGHTS: District of Columbia Office of Zoning, Department of Buildings, Office of the Surveyor, Office of Tax and Revenue, OCTO GIS and originating agencies identified in metadata. Underlying source data are CC BY 4.0, https://creativecommons.org/licenses/by/4.0/. LandSight added normalization, relationships, measured spatial screening and review queues. No government endorsement is implied. Underlying CC BY rights are not restricted by LandSight paid-curation terms.