Seychelles Building Import

Goals

The goal is to add the outlines of most of the buildings on the three main inner islands of the Seychelles (i.e. Mahe, Praslin and La Digue) to OSM, as well as some few buildings for the remaining inner islands. This is to complement the building information already available on OSM for the Seychelles. In addition to the building outlines there is information available for a significant number of buildings on whether they are residential. While the building outlines have been digitised by the Centre for GIS from a high resolution aerial photo the National Bureau of Statistics has added building details primarily (such as residential).

Schedule

The import is planned to be done at the end of the second week of August, 2018. A previous notification and a discussion has taken place on the imports list.

Import Data

Background

Source 1)

Centre for GIS / Ministry of Habitat, Infrastructure and Land Transport (MHILT) of the Republic of Seychelles

Data source site: https://www.webgis.gov.sc/introduction.phtml
Data license: ODbL
Data release letter/agreement: https://www.dropbox.com/s/p97my7ajqgefoar/Open%20Street%20Map%20Release%20Letter%20Centre%20for%20GIS_Seychelles.pdf?dl=0
ODbL Compliance verified: yes

Source 2)

National Bureau of Statistics of the Republic of Seychelles

Data source site: https://www.nbs.gov.sc
Data license: ODbL
Data release letter/agreement: https://www.dropbox.com/s/0ui75y5zsxolwyg/Open%20Street%20Map%20Release%20Letter%20NBS_Seychelles.pdf?dl=0
ODbL Compliance verified: yes

Source/Original Data Files

The original data can be downloaded here.

OSM Data Files

A new OSM file has been generated ("seychelles_buildings.osm") containing the buildings to be added (about 31,000).

Import Type

This is meant to be a one-time import. The long-term plan is to encourage various government (and other) organisations to update building information on OSM regularly so that another bulk import would not be necessary. Data will be imported into the OSM database using JOSM.

Data Preparation

Data Reduction & Simplification

1.) Existing OSM data for the Seychelles was downloaded using QGIS and the OSMDownloader plugin.
2.) A query was performed to separate the buildings from other OSM data.
3.) Overlapping buildings and buildings with invalid geometry were identified in the government dataset and removed.
4.) A query was performed to remove from the government dataset those buildings that are already in the OSM database.

Tagging Plans

The building outlines will be tagged as follows:

• building=residential (where that detail is available)
  
• building=yes (all other buildings)
  

Changeset Tags

source=Centre for GIS | National Bureau of Statistics, Republic of Seychelles
type=import
url=https://wiki.openstreetmap.org/wiki/Seychelles_Building_Import

Data Transformation

The original government dataset was available in Shapefile format. The Shapefile was then modified and cleaned. All attributes not to be imported were removed. Using the "opendata" plugin the Shapefile was loaded into JOSM directly and was saved in OSM format. Further validation and cleaning was then performed using JOSM.

Data Transformation Results

seychelles_buildings.osm

Data Merge Workflow

Team Approach

So far I intend to perform the whole import myself since there is no OSM community established yet in the Seychelles. I am the administrator of talk-sc.

Workflow

1.) Existing OSM data for the Seychelles was downloaded using QGIS and the OSMDownloader plugin.
2.) A query was performed to separate the buildings from other OSM data.
3.) A query was performed to remove from the government dataset those buildings that are already in the OSM database.
4.) An attribute "building" was assigned to the government dataset and given the values "residential" or "yes" based on the "use" type information available for the buildings.
5.) The government dataset was exported to Shapefile format.
7.) The Shapefile with buildings (government dataset) was loaded into JOSM (using the "opendata" plugin).
8.) All buildings from the Shapefile layer were copied and pasted into a new OSM data layer.
9.) Basic data verification was performed using the JOSM validation tool.
10.) The OSM data layer with the buildings was saved as "seychelles_buildings.osm" and is ready for review.

• Changeset size policy: Data will be uploaded in chunks (one changeset per island). That should make it easier to revert changes.
• Revert plans: All buildings will be imported using a user account created solely for the import (info@allspatial.info) which will facilitate a revert should it be required.

Conflation

Conflation and preventing relating data conflicts is covered by an appropriate import workflow (see the Workflow section above). That means only missing buildings are imported, existing data is left untouched.

QA

1.) Overlapping buildings were removed from the government dataset.
2.) Buildings with invalid geometries were removed from the government dataset.
3.) Duplicate vertexes were removed from buildings in the government dataset.
4.) Basic data verification was performed using the JOSM validation tool and data was cleaned accordingly.

See also

The email to the Imports mailing list was sent on 2018-08-05 and can be found in the archives of the mailing list at [1].