Connecticut/CT Buildings Update 2023

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STATUS: In preparation

Duration: NA

Current progress: 0%

Participating users: Mashin

Import account: CT-import

Changeset comment: #CT-building-update-2023

For comments send PM to OSM account Mashin or leave a message at OSMUS Slack channel #local-connecticut.

Rationale

Previous import of building footprints for Connecticut was based on data from 2016. Since then many changes many buildings were extended, demolished or newly built. In 2023, State of Connecticut ordered new set of areal imagery and LiDAR data in high resolution. Height data from LiDAR was processed into building footprints and made publicly available under CC0 license: https://data.ct.gov/dataset/2D-Building-Footprints/utqj-vrdu

Data

New building footprint data was downloaded from data.ct.gov and compared to OSM buildings state on date 22-JAN-2026.
Code is available: GitHub

Processing

New Buildings

Any 2023 polygons that don't overlap with OSM polygons.

  • 183,994 candidates
  • 31,659 big buildings (>100m2) + 152,335 small buildings (<100m2)
  • Polygons that don't overlap with buildings currently in OSM
  • Contains: Newly built buildings, sheds, old structures missed in old dataset
  • Errors: Trucks and RVs, trees, hedges, incomplete footprints if building was obstructed by a tree

Demolished Buildings

OSM buildings larger than 100m2 that have no overlapping polygon in new dataset

  • 17,041 candidates
  • Contains: buildings that were demolished
  • Errors: buildings that stil exist but were not captured by LiDAR processing

Changed Buildings

  • 39,695 candidates
  • 16,137 modified buildings + 23,558 bad old import shapes
  • Contains: houses with built extensions, old import shapes
  • Errors: bad or rotate building shapes


Licence

Data is released under CC0 1.0 Universal license compatible with OSM's ODbL.

Strategy

Data import will be done in JOSM with manual review.

  • Commit message: #CT-building-update-2023
  • Commit source: State of Connecticut
  • Add Changeset tag: documentation = wiki.openstreetmap.org/wiki/Connecticut/CT_Buildings_Update_2023

Requirements

JOSM with plugins:

  • Conflator plugin
  • TODO plugin
  • Continuous download
  • Utils plugin 2 / replace geometry

Guideline

New Buildings

  1. Select bunch of new buildings from the import layer (find: type:way building)
  2. Paste them into OSM data layer (CTRL + SHIFT + V)
  3. Add them to TODO list
  4. Turn on continuos download
  5. Cycle through them one-by-one : Adjust shape, delete false positives, remove if already added

False positives could be:

  • trees
  • cars
  • hedges
  • someone has already added the building in the mean time
  • watch out for bad shapes
  • merged multiple buildings

Demolished Buildings

  1. Select buildings in import layer (find: type:way building)
  2. Add them to TODO list
  3. Switch to OSM layer and turn on continuous download
  4. Cycle through one-by-one: make sure building is not there in CTECO_2023 and MapBox


false positives could be:

  • Buildings that are being built, but someone added the sape based on visible foundation
  • Buildings visible in newer imagery e.g. Mapbox

Modified buildings

  1. Use conflator plugin
  2. Select buildings on OSM layer and 'freeze' them as reference
  3. Select buildings in import layer and 'freeze them as subject
  4. Set centroid distance to < 30 m, tick 'Replace Geometry', tick 'Merge tags - All' and Generate matches
  5. Cycle through one-by-one: conflate if new shape is better
  6. Adjust shape if it still deviates from the real object in imagery
Retrieved from "https://wiki.openstreetmap.org/w/index.php?title=Connecticut/CT_Buildings_Update_2023&oldid=2956741"