This project will improve the OSM basemap for the city of Dallas, Texas using the data available for download from the City of Dallas GIS Services. Available data includes building footprints, parks and trails, and hydrologic features.
Data Usage Permissions
The City of Dallas GIS Services department was contacted on November 30, 2016, and the following reply was received confirming that the data license is compatible with OSM usage:
"We provide the data without restriction or guarantees of fitness for any purposes. We don't have any authority to grant or recognize the use of the data for any particular purpose(s). We consider it to fall under the heading of "public information", so it is available to use as you see fit. Perhaps you might use the Texas Public Information Act for your citation. Once you download the data, it is yours and we assume no responsibility or liability. Per State Law, we fully disclaim its use for any and all purposes. Regards, Michael R Miller, GIS Technical Manager, Communications & Information Services, Innovation & Information Management Services, City GIS Services, Michael.Miller2@DallasCityHall.com, 214.670.0876"
This response has also been documented on the Potential Datasources page.
The project will follow this roadmap to completion
- Identify useful data to be imported into OSM
- Create and document workflow
- Implement test, modify workflow as needed, and document results
- Begin city-wide import
This page will be updated as the project progresses to keep the OSM community informed.
All imports will contain the #DallasImport tag in their changeset comments.
The City of Dallas GIS Services has produced building footprints digitized from 2009 aerial photography that is suitable for import into OSM.
Buildings will be imported in stages in manageable sizes based on city block or neighborhood. This will allow the work to be prioritized while also keeping the imports manageable for verification.
Buildings will be processed and tagged using the following procedure:
- Use parcel data to prepare buildings in GIS software - the up-to-date Parcels layer contains a building classification field ("BLDG_CL") in the shapefile that can be used to tag the building.
- Dissolve the parcel data by the building classification field.
- Match building classification values to appropriate OSM tags. For example, buildings on parcels with a building classification of "SCHOOL" would be tagged as building=school, those with "CHURCH BUILDING" would be tagged building=church
- In the case where a building footprint overlaps several parcels (the number of features the building was spatially joined to exceeds 1), and the uses conflict with OSM tagging, the building=yes tag will be used.
- Buildings that fall on parcels with the building classification "LAND ONLY" will be flagged and reviewed during validation - these likely represent buildings that have been torn down since 2009.
- Use other City of Dallas point data to further differentiate buildings - Various point layers such as fire stations and libraries intersect with their buildings. These can be tagged appropriately.
- Drop any unneeded attributes from the GIS files.
- Import GIS file into JOSM
- Select features by its intended tag, copy into appropriate layer, and tag appropriately.
- Validate (see below)
- Repeat process for remaining buildings.
Imports will be checked with these steps before upload to OSM servers:
- Comparing the building footprints from 2009 with the Texas Orthophoto layer (taken in 2015) to ensure no significant changes have occurred (i.e. buildings torn down and/or new buildings constructed)
- Comparing building footprint with any existing buildings in OSM. If the OSM building is largely consistent, the building will not be imported. The Replace Geometry tool will be used to maintain the history of buildings already existing, but copying new geometry and tags over to the feature
- Running the upload through JOSM Validator to resolve any remaining issues, such as overlapping buildings or buildings overlapping ways
Missing park boundaries are being imported from Dallas shapefiles. If a park is already satisfactorily mapped, it will not be imported.
The test area for this project will be Fair Park, a key neighborhood in the city's economic and community development efforts and an ideal location given the relative lack of OSM data in the area.
Test #1 - Buildings (Except Single Family)
- Buildings were able to be easily imported and tagged based on the steps in the workflow
- Imported buildings passed JOSM Validation
- Single family buildings were just as easy to import, but validating them against imagery is more time-consuming and will be done in a later phase.
- Test revealed the need for validation to improve OSM data in South Dallas
- Parcel data could be used to improve locations of places of worship
Test #2 - Tag Check
All 438,722 building footprints were processed with the workflow. 17,739 were flagged as overlapping a parcel with no building and will be checked separately. A summary of the identified tags to be imported is shown below:
|building=||# buildings||amenity=||# buildings|
January 2 - Test imports succeed
January 13 - So far 38,402 (8.7%) of the building footprints have been imported, resulting in 36,170 buildings being added. The remaining imports will first skip houses to focus on commercial buildings, then will circle back to finish remaining houses. Deep Ellum and Lower Greenville need to be reviewed to remove any sheds that were imported and clutter the map.
January 17 - 101,801 (23.2%) of footprints have been processed, creating 98,794 buildings.